Compositions, systems and methods for producing nanoalloys and/or nanocomposites using tandem laser ablation synthesis in solution-galvanic replacement reaction

ABSTRACT

Compositions, systems, and methods for producing nanoalloys and/or nanocomposites using tandem laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) are disclosed. The method may include disposing a first metal composition within a reaction cell, adding a quantity of a second metal composition into the reaction cell, ablating, with a laser, the first metal composition disposed in the quantity of the second metal composition within the reaction cell, and tuning one or more reaction parameter and/or one or more functional parameter during the tandem LASiS-GRR in order to tailor at least one characteristic of the metal nanoalloy and/or the metal nanocomposite.

TECHNICAL FIELD

The presently disclosed subject matter relates generally to tandem laserablation synthesis in solution-galvanic replacement reaction (LASiS-GRR)techniques. In some embodiments, the presently disclosed subject matterrelates to compositions, systems, and methods for producing nanoalloysand nanocomposites using tandem LASiS-GRR.

BACKGROUND

Energetically expensive oxygen reduction reactions (ORR) at the cathodehave been the rate determining step and hence, a severe hindrance toefficient and clean electrochemical energy conversions inlow-temperature proton exchange membrane fuel cells (PEMFCs) [1-7]. Topromote the ORR activities, Pt based nanocatalysts have largely beenused for most commercial applications [6, 8-10]. Yet, the cost ofprecious metal based catalysts added to the lack of stability anddurability of Pt under the highly corrosive and acidic conditions offuel cell operations have prompted a large volume of research in recentyears geared towards the development of transition metal based alloysand/or, intermetallic materials with low Pt-loading [11-16].Specifically, recent U.S. DRIVE fuel cell technical roadmap hasestablished the 2020 target for the total loading of Pt group metals(PGM) to be approximately 0.125 mg/cm² electrode area for PEMFCelectrocatalysts [17]. To this end, alloyed nanocatalysts have gainedtremendous research interest in the past decade due to their uniquegeometric and/or electronic characteristics that dramatically enhancetheir catalytic activities, while reducing the net PGM content [18-24].Alloying Pt with transition metals such as Co, Ni, Cu, etc., have beenfound to effectively shrink the lattice constant (geometric effect) andtune the d-band center (electronic effect), resulting in a moderateoxygen binding energy (eV) and consequently improved specific and massactivities for electrocatalytic ORR processes [3, 19, 20, 25-28].

Among the aforementioned Pt based nanoalloys (NAs), PtCo systems haveattracted the most attention due to its relatively higher activity andstability for the ORR process [5, 29-36]. The nominal Pt:Co ratio aswell as the degree of alloying in these nanocatalysts play a criticalrole in tuning the nanoscale crystalline structures and band structureswhich in turn dictate the aforementioned geometric and electroniceffects responsible for tailoring their ORR catalytic activities [4, 37,38, 30]. Conventional PtCo alloys were usually prepared by simultaneousreduction of cobalt salts (e.g., Co(NO₃)₂, CoCl₂) and platinumprecursors (Pt(acac)₂, K₂PtCl₄, H₂PtCl₄) in either organic or aqueousconditions, and almost always involve the use of external andindispensible stabilizing agents (CTAB, PVP, oleylamine, etc.) [1, 37,34]. Recently, a wide range of synthesis techniques have been developedthat include impregnation [30], solvothermal method [39], tandemdecomposition and chemical reduction [22], polyol method [40], reversemicelle method [41], replacement reaction [42], etc. Yet, most of thosesynthesis techniques involve wet chemical routes that require intricatesteps and even these techniques inevitably use harsh unwanted chemicalsin the form of surfactants and/or, stabilizing agents. These organicresidues on the nanoparticle (NP) surface are detrimental to theirinterfacial catalytic properties and eventually, systematic removal ofthose organic encapsulations from these alloyed and/or intermetallic NPsbecomes a challenging and critical step in itself for large-scaleproduction of nanocatalysts. Besides, a fine control of the Pt:Co atomicratios and alloying degrees for systematic synthesis of a wide range ofnanocatalysts still remains elusive in most of these techniques, therebyrestricting the application of these ORR catalysts to only limitedenvironmental conditions [5, 41, 38, 40, 43].

Additionally, a few recent attempts have synthesized designernanocomposites (NCs) made from the best of both ORR (e.g., Pt NPs) andoxygen evolution reaction (OER) catalysts (e.g., transition metaloxides) However, clean synthesis of these complex nanocatalysts in afacile, cheap, and reproducible manner still remains elusive. Even here,most synthesis techniques for metal and metal oxide NPs involve wetchemical routes that require intricate experimental steps involvingindispensable chemicals such as surfactants, organic ligands, reducingagents, etc. that block their active surface catalytic sites. [30, 63,64, 65] Many metal/metal oxide NCs made from perkovsite based oxides arecomplicated to synthesize and require multi-step processes with harshchemical conditions and residues. [66, 67, 68] Finally, removal oforganic encapsulation (ligands and/or surfactants) from metal/metaloxide NPs itself is a challenging and critical step in theirpreparation. [69]

As a consequence, compositions, systems, and methods for producing NAsand/or NCs that allow precise construction of inter-atomic structuresand extent of alloying in facile, cheap, and reproducible manners areneeded.

SUMMARY

This summary lists several embodiments of the presently disclosedsubject matter, and in many cases lists variations and permutations ofthese embodiments. This summary is merely exemplary of the numerous andvaried embodiments. Mention of one or more representative features of agiven embodiment is likewise exemplary. Such an embodiment can typicallyexist with or without the feature(s) mentioned; likewise, those featurescan be applied to other embodiments of the presently disclosed subjectmatter, whether listed in this summary or not. To avoid excessiverepetition, this summary does not list or suggest all possiblecombinations of such features.

In some embodiments, a method for producing a metal nanoalloy and/or ametal nanocomposite using tandem laser ablation synthesis insolution-galvanic replacement reaction (LASiS-GRR) is provided herein.The method may comprise disposing a first metal composition within areaction cell, adding a quantity of a second metal composition into thereaction cell, ablating, with a laser, the first metal compositiondisposed in the quantity of the second metal composition within thereaction cell, and tuning one or more reaction parameter and/or one ormore functional parameter during the tandem LASiS-GRR in order to tailorat least one characteristic of the metal nanoalloy and/or the metalnanocomposite.

In other embodiments, a system for producing a metal nanoalloy and/or ametal nanocomposite using tandem LASiS-GRR is provided herein. Thesystem may comprise a reaction cell, a first metal composition disposedwithin the reaction cell, a quantity of a second metal compositionconfigured to be added into the reaction cell, and a laser configured toablate the first metal composition disposed in the quantity of thesecond metal composition within the reaction cell, wherein the system isconfigured such that one or more reaction parameter and/or one or morefunctional parameter is tuned during the tandem LASiS-GRR in order totailor at least one characteristic of the metal nanoalloy and/or themetal nanocomposite.

In further embodiments, a metal heteronanostructure is provided herein.In some embodiments, the metal heteronanostructure may comprise asubstantially uniform alloyed core of a first metal and at least onesecond metal, and a shell or matrix surrounding the substantiallyuniform alloyed core, the shell or matrix comprising one of the firstmetal and at least one second metal.

In still further embodiments, a substantially uniform nanoalloy isprovided herein. The metal nanoalloy may comprise a first metal and atleast one second metal, wherein the first metal is a precious metal andthe second metal is a non-precious, transition metal, and wherein adegree of alloying is approximately between 40-60%.

Also provided is a catalyst composition comprising a nanocompositeand/or nanoalloy as described herein.

Accordingly, it is an object of the presently disclosed subject matterto provide new methods, systems and compositions for the production ofnanoalloys such as PtCo and nanocomposites such as PtCo/CoOx. Theseobjects and other objects are achieved in whole or in part by thepresently disclosed subject matter.

An object of the presently disclosed subject matter having been statedhereinabove, and which is achieved in whole or in part by the presentlydisclosed subject matter, other objects will become evident as thedescription proceeds when taken in connection with the accompanyingdrawings and examples as best described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 depicts a schematic of a system for producing a metal nanoalloyand/or a metal nanocomposite using tandem laser ablation synthesis insolution-galvanic replacement reaction (LASiS-GRR);

FIG. 2 depicts a flow diagram of a method for producing a metalnanoalloy and/or a metal nanocomposite using tandem LASiS-GRR;

FIGS. 3A-3D depict transmission electron microscope (TEM) images withselected area electron diffraction (SAED) images inset of four differentPtCo nanoalloy samples PtCo-1, PtCo-2, PtCo-3, PtCo-4, respectively, assynthesized by tandem LASiS-GRR for various K₂PtCl₄ concentrations andablation times;

FIG. 4 depicts a graphical comparison of x-ray diffraction (XRD)patterns for different PtCo nanoalloy samples PtCo-1, PtCo-2, PtCo-3,PtCo-4, respectively, as synthesized by tandem LASiS-GRR for variousK₂PtCl₄ concentrations and ablation times;

FIG. 5A depicts an energy dispersive x-ray spectroscopy (EDX) elementalmapping result for a PtCo-2 sample as synthesized by tandem LASiS-GRR;

FIGS. 5B-5C depict EDX elemental mapping results for Pt and Co,respectively, in the PtCo-2 sample of FIG. 5A;

FIG. 5D depicts an electron energy-loss spectroscopy (EELs) analysiselemental mapping result for a PtCo-2 sample (inset) as synthesized bytandem LASiS-GRR;

FIGS. 5E-5F depict EELs analysis elemental mapping results for Pt andCo, respectively, in the PtCo-2 sample of FIG. 5D;

FIG. 5G depicts an EELs analysis elemental mapping result illustratingthe Pt/Co atomic ratio for the PtCo-2 sample from FIGS. 5E-5F;

FIG. 5H depicts a graphical representation of a Pt atomic ratio (%)distribution across the line scan across the dashed line illustrated inFIG. 5G;

FIG. 6 depicts a graphical comparison of x-ray diffraction (XRD)patterns for different PtCo nanoalloy samples PtCo-1, PtCo-2, PtCo-3,PtCo-4, respectively, as synthesized by tandem LASiS-GRR for various PHconditions and same initial K₂PtCl₄ concentrations and ablation times;

FIG. 7A depicts cyclic voltammetry curves at a scan rate of 50 mV/s fordifferent PtCo nanoalloy samples PtCo-1, PtCo-2, PtCo-3, PtCo-4,respectively, as synthesized by tandem LASiS-GRR;

FIG. 7B depicts linear sweep voltammagrams for oxygen reductionreactions (ORR) polarization curves in 0.1M HClO₄ electrolyte saturatedwith dissolved O₂ at 1600 rpm and scan rate of 5 mV/s for different PtConanoalloy samples PtCo-1, PtCo-2, PtCo-3, PtCo-4, respectively, assynthesized by tandem LASiS-GRR;

FIG. 7C depicts Koutecky-Levich plots from rotating disk voltammogram(RDV) data (inset) for a PtCo-2 sample at different potentials(0.70-0.87 V) indicating a four electron transport process for ORR;

FIG. 7D depicts Tafel plots for different PtCo nanoalloy samples PtCo-1,PtCo-2, PtCo-3, PtCo-4, respectively, as synthesized by tandem LASiS-GRRas well as Pt/C;

FIG. 7E depicts a graphical representation of a comparison of massactivity and specific activity at 0.9 V vs. reversible hydrogenelectrode (RHE) for different PtCo nanoalloy samples PtCo-1, PtCo-2,PtCo-3, PtCo-4, respectively, as synthesized by tandem LASiS-GRR, aswell as Pt/C;

FIG. 7F depicts cyclic voltammetry curves indicating the %electrochemical surface area (ECSA) values and Co ratio (%) in an alloyafter various numbers of potential cycles at a scan rate of 100 mV/s;

FIG. 8A depicts cyclic voltametry curves at a scan rate of 50 mV/S fordifferent PtCo nanoalloy samples synthesized by tandem LASiS-GRR atdifferent pH conditions;

FIG. 8B depicts linear sweep voltammograms for ORR analysis in 0.1 MHClO₄ electrolyte saturated with dissolved O₂ at 1600 rpm and scan rateof 5 mV/s for different PtCo nanoalloy samples synthesized by tandemLASiS-GRR at different pH conditions;

FIG. 8C depicts a Tafel plot corresponding to FIG. 8B;

FIG. 8D depicts a comparison of mass activity and specific activity at0.9 V vs. RHE;

FIG. 9 depicts a schematic diagram indicating the synthesis of PtConanoalloys by tandem LASiS-GRR using different initial Pt²⁺concentrations and pH conditions;

FIGS. 10A-10D depict TEM images with SAED images inset of four differentPtCo nanocomposite samples PtCo-5, PtCo-6, PtCo-7, PtCo-8, respectively,as synthesized by tandem LASiS-GRR for various K₂PtCl₄ concentrations;

FIGS. 10E-10H depict size distributions for darker spherical Pt-basedNPs corresponding to the PtCo nanocomposite samples in FIGS. 10A-10D,respectively;

FIG. 11A depicts high resolution transmission electron microscopy(HRTEM) images of the PtCo-5 sample with corresponding positions (b-d)marked to indicate lattice fringes;

FIGS. 11B-11D depict HRTEM images of the corresponding positions (b-d)in FIG. 11A, respectively;

FIG. 12A depicts a high-angle annular dark-field (HAADF) image for thePtCo-7 sample;

FIGS. 12B-12D depict corresponding elemental mappings for Pt, Co and O,respectively, of the PtCo-7 sample of FIG. 12A;

FIGS. 12E-12F depict graphical representations of spectra e, f,respectively, illustrated in FIG. 12A;

FIG. 13 depicts XRD data for PtCo/CoO_(x) NCs dispersed in carbon black(CB);

FIG. 14A depicts a graphical representation of ORR catalytic performancefor each of the catalyst samples under study through the linear sweepvoltammogram (LSV) test;

FIG. 14B depicts a graphical representation of a comparison of the Tafelplots for the samples generated from FIG. 14A over low overpotentialregions;

FIG. 14C depicts a graphical representation of a comparison of massactivities per unit Pt loading amount at 0.85 V vs. RHE for thePtCo/CoO_(x) NCs studied;

FIG. 14D depicts a graphical representation of slopes for the KL plotsgenerated from rotation-rate dependent current-potential curves (insetin FIG. 14D) for the PtCo-7 NCs in the range of 0.70-0.83 V;

FIG. 14E depicts a graphical representation of a comparison ofnormalized current density (%) at the corresponding half-wave potentialsfor the Co₃O₄, PtCo-7, and standard Pt/C samples;

FIGS. 15A-15B depict graphical representations of OER catalyticactivities for PtCo-5, PtCo-6, PtCo-7, and PtCo-8 compared against pureCo₃O₄ and standard Pt/C samples;

FIGS. 15C-15D depict graphical representations of combinedoverpotentials for PtCo-5, PtCo-6, PtCo-7, and PtCo-8 compared againstpure Co₃O₄ and standard Pt/C samples;

FIG. 16 depicts a schematic illustrating the synergic “spill-over”effects responsible for the site-specific adsorption/desorption of thedesired species to promote bifunctional catalytic performances in NCsproduced using tandem LASiS-GRR;

FIGS. 17A-17D depict TEM images of nanostructures formed in the productsof LASiS and the resulting lattice planes;

FIG. 18A depicts a HAADF image of the sample synthesized via LASiS on Znin AgNO₃;

FIGS. 18B-18D depict the corresponding Ag, Zn and O elemental mappings,respectively, of the sample in FIG. 18A;

FIG. 19A depicts a HAADF image of the sample synthesized via LASiS on Tiin AgNO₃ after an HNO₃ wash;

FIGS. 19B-19C depict an enlarged HAADF image and elemental mapping ofFIG. 19A, respectively;

FIG. 19D depicts the sample illustrated in FIG. 19A after re-irradiation(RI) treatment;

FIGS. 19E-19F depict an enlarged HAADF image and an EDX mapping of FIG.19D, respectively;

FIG. 20A depicts an XRD profile comparing TiAg against standard Ag;

FIG. 20B depicts an XRD profile comparing ZnAg against standard Ag andstandard ZnO₂;

FIGS. 21A-21B depict graphical representations of UV-Vis absorbance;

FIG. 22A depicts a TEM image for a sample PtCuCo-2 ternary alloysynthesized via tandem LASiS-GRR;

FIG. 22B depicts an EDX mapping of a sample of the PtCuCo-2 ternaryalloy synthesized via tandem LASiS-GRR, as illustrated from FIG. 22A;

FIG. 22C depicts a corresponding EDX mapping of Pt from FIG. 22B;

FIG. 22D depicts a SAED image at a scale of 5 (1/nm) of the PtCuCo-2ternary alloy;

FIG. 22E depicts a corresponding EDX mapping of Cu from FIG. 22B;

FIG. 22F depicts a corresponding EDX mapping of Co from FIG. 22B;

FIG. 23 depicts a graphical representation of elemental compositions ofternary alloys with a change of laser ablation time; and

FIG. 24 depicts an XRD profile for PtCuCo NAs by identification of thePt characteristic peak shift to higher 2-theta angles.

DETAILED DESCRIPTION

Laser ablation synthesis in solution-galvanic replacement reaction(LASiS-GRR) is provided as a green synthesis technique for manufacturingnanoalloys as, for example, excellent oxygen reduction reaction (ORR)catalysts in acid electrolytes, and/or, nanocomposites as superiorbifunctional catalysts for both ORR and oxygen evolution reaction (OER)in alkaline media for fuel cell applications. In some embodiments, theterms “nanoalloy” and “nanocomposite” are used herein in a manner thatis consistent with how one of ordinary skill in the art of the inventionwould understand these terms. By way of elaboration, the term“nanoalloy” or “NA” is defined as a uniform mixture of two or multiplemetals in nano-size (in some embodiments, within 100 nm) with uniquecrystal structure and lattice spacing different from the individualparent metal components, while the term “nanocomposite” or “NC” isdefined as a multiphase material (comprised of either pure materials orcompounds) with each phase in a nano-size range. The term“heteronanostructure” refers generally to a “composition” or“nanocomposition” such as, for example, a nanoalloy or a nanocompositeas described herein.

The terms “nano”, “nano-sized”, “nanoscale”, “nanomaterial” and“nanoparticle” refer to a structure having at least one region with adimension (e.g., length, width, diameter, etc.) of less than about 1,000nm. In some embodiments, the dimension is smaller (e.g., less than about500 nm, less than about 250 nm, less than about 200 nm, less than about150 nm, less than about 125 nm, less than about 100 nm, less than about80 nm, less than about 70 nm, less than about 60 nm, less than about 50nm, less than about 40 nm, less than about 30 nm, less than about 20 nm,or even less than about 10 nm). In some embodiments, the dimension isbetween about 1 nm and about 100 nm (e.g., about 1, 2, 3, 4, 5, 10, 20,30, 40, 50, 60, 70, 80, 90, or 100 nm).

In some embodiments, systems and methods described herein provide animproved and modified LASiS-GRR technique to synthesize pure metal NAsthat exhibit excellent ORR activities in acid electrolyte solutions.More particularly, performing LASiS-GRR in tandem (i.e., simultaneously)rather than in succession or individually provides a facile, green, yetefficient route to synthesize metal NAs with tailorable sizes,compositions, and/or degrees of alloying by way of tuning one or morereaction and/or functional parameter during tandem LASiS-GRR.

In principle, LASiS involves a liquid-confined plasma plume expandingwith extremely high temperatures and pressures (c.a. 10³ K and 10⁹ Parespectively) [50] that thermally vaporizes a metal target and initiatesultrafast propagation of cavitation bubbles. Typically, these cavitationbubbles contain the nucleated seeding nanoparticles (NP)s that finallyundergo rapid collisional quenching at the bubble-liquid interface [45,50-54], while initiating simultaneous chemical reduction reactions withthe solutions phase precursors and/or species. However, LASiS performedindividually has some disadvantages, including an inability toaccurately control the structure and morphology of the synthesizednanomaterial during LASiS.

Accordingly, tandem LASiS-GRR is disclosed herein in order to overcomethe limitations inherent in LASiS by performing LASiS in tandem withGRR. In this manner, the inability to accurately control the structureand morphology of the synthesized nanomaterial during LASiS is overcomevia GRR at the plasma cavitation-liquid interface that is essentiallyinitiated by the rate-limiting source production of metal target NPs viaLASiS without the need for any surfactants and/or stabilizing agentsthat are potentially harmful for surface catalytic activities [55]. Indoing so, the amount of reduced precious metal NPs that alloy with theseeding metal target NPs is tuned, thereby tailoring the composition,structure and degree of alloying in the resulting NA samples. Thus,different extents of alloying in the aforementioned NAs and in turntheir catalytic properties are systematically controlled in a simpleyet, elegant fashion by tuning the relative rates of one or morereaction and/or functional parameter during tandem LASiS-GRR.

Particularly, the compositions, systems, and methods disclosed hereinmay be used to synthesize specific metal NAs and/or NCs without externalstabilizing agents. As disclosed herein, resultant metal NAs producedfrom tandem LASiS-GRR from a first metal composition and at least onesecond metal composition may exhibit substantially uniformly alloyedcores with a metal-rich shell of a few nanometers. Such a core-shellstructure along with high degrees of alloying in these metal NAs may beconfigured with outstanding electrocatalytic ORR activities in acidelectrolytes, to be discussed in more detail below, which are attributedto the efficacy of tandem LASiS-GRR route to rationally tune sizedistributions and/or compositional ratios and alloying degrees of theNAs and/or NCs without the use of any surfactants or reducing agentsthat are otherwise indispensable in chemical synthesis methods, butharmful for catalytic performances.

FIG. 1 illustrates a schematic of a system, generally designated 100,for producing a metal NA or NC using tandem LASiS-GRR. In some aspects,system 100 may include a reaction cell 102, a first metal composition,generally designated 104, comprising a non-precious, transition metaltarget disposed within the reaction cell 102, a second metalcomposition, generally designated 106, comprising a quantity of asolution of one or more precious metal salt precursor configured to beinjected into the reaction cell 102, and a laser 110 configured toablate the non-precious, transition metal target 104 disposed in thequantity of the precious metal salt solution 106 for a period of timewithin the reaction cell 102. In some aspects, the system 100 mayfurther comprise an injection unit 108 and/or a motor 112, as well as,but in no way limited to, one or more of heating coil(s), awashing/decanting centrifuge unit, a dryer unit (e.g., a diffusiondryer), a thermocouple, and/or an ultrasonicator.

The reaction cell 100 may be configured as a partially enclosed space inwhich at least the first and second metal compositions (i.e., thenon-precious transition metal target and the precious metal saltprecursor) 104, 106 may be contained for control and/or tenability ofone or more reaction and/or functional parameter during tandem LASiS-GRRso as to tailor specific characteristics of an NC and/or NA and henceoptimize its catalytic properties. In some aspects, the reaction cell102 may be a cell configured to allow for injections of the quantity ofa solution of one or more precious metal salt precursor 106. Thereaction cell 102 may be configured to enable gas and/or temperaturecontrol, which may be tunable as one or more environmental parameterduring LASiS-GRR. For example, purging N₂ and O₂ from the reaction cellmay result in formation of Co(OH)₂ and CoO respectively during LASiS onCo; while high temperature LASiS may lead to a much faster phasetransfer for the produced metastable species into higher oxidationstates. The reaction cell 102 may also be configured to receive acontinuous supply of the quantity of the metal salt solution 106 throughan injection unit 108. More particularly, a continuous supply of thequantity of metal salt 106 at a controlled speed through an injectionunit 108 may enable mass production of NCs through tandem LASiS-GRR. Amounted probe ultrasonicator (not shown) may provide simultaneousultrasonication that may quickly disperse newly injected precious metalsalt solution 106 and prevent an ablated species from aggregation. As aresult, a high surface to volume ratio for ORR and/or OER activities maybe maintained for the products. One or more heating coil (not shown) maybe provided on a bottom surface of reaction cell 102 in order to heatthe quantity of the metal salt solution 106 and/or the target 104. Otherfunctional and/or reaction parameters may also be tuned via the reactioncell 102.

The quantity of a solution of one or more precious metal salt precursor106 may be a solution-phase metal precursor mixed with water. Forexample, the solution-phase metal precursor may be K₂PtCl₄ (>99.9%) inde-ionized water (DI-water; Purity=99.9%; Conductivity=18.2 MΩ/cm at 25°C.). Different concentrations of the precious metal salt solution 106,such as 125, 250, 375, and 500 mg/l may be tuned in order to tailor atleast one characteristic of the metal NA. In some aspects, the quantityof a solution of one or more precious metal salt precursor 106 may bebubbled with another element, e.g., N₂, for a period of time afterinjection into the reaction cell 102. For example, the period of timemay be 30 minutes.

A non-precious, transition metal target 104 may be formed as a pelletand disposed within the reaction cell 102. For example, a Co pellethaving 99.95% purity, ¼″ diameter×¼″ height may be utilized. The pellet104 may undergo a period of ablation at which point a laser 110, e.g., a1064 nm laser (330 mJ/pulse, 10 Hz) may ablate the pellet 104 andproduce seeding metal NPs. The laser 110 may be configured as a pulsedor a continuous laser having different laser energy, wavelength,duration time, etc. For example, the laser 110 may be an Nd:YAG pulsedlaser configured to emit 532 nm (165 mJ/pulse) and/or 1065 nm (330mJ/pulse). Tuning the laser 110 to ablate the target 104 for a differentablation time may result in tailoring at least one characteristic of themetal NA, such as the size, morphology, shape, etc. For example, anablation time of 4, 7, 13, and 20 minutes may be used and may bepredetermined in order to achieve a specified percent reduction (e.g.,60% reduction) in the initial solution-phase metal precursor in thequantity of a solution of one or more precious metal salt precursor 106.In some aspects, the non-precious, transition metal target 104 may berotated during ablation. For example, the target 104 may be rotated by astepper motor 112 at a uniform speed of 0.3 rpm during ablation.

Ablation of the non-precious, transition target 104 may result inproduction of a colloidal solution having a specific pH value. The pHvalue of the colloidal solution may be adjusted to be more acidic ormore alkaline. For example, the pH value of the colloidal solution maybe decreased by adding acid (e.g., HCl, KOH) to the solution. Tuning thepH value in this manner may also result in tailoring at least onecharacteristic of the metal NA, such as the size, morphology, shape,etc.

After tandem LASiS-GRR, the metal NAs may be collected and decantedusing for example, a centrifuge (not shown) mixed with a high pressureinert gas. For example, the metal NAs may be centrifuged at 4700 for 15minutes and decanted by washing with DI-water. Afterwards, the metal NAsmay be re-dispersed in either water or ethanol, and then mixed withcarbon black for producing fuel cell catalysts. Thus, in someembodiments, provided are catalyst compositions comprising ananocomposite and/or nanoalloy in accordance with the presentlydisclosed subject matter.

Notably, during tandem LASiS-GRR at the liquid front, the target 104 mayundergo competing reactions. For example, the reactions include: (1)Reactions with the solution-phase H⁺ ions from water; and/or (2) GRRwith ions from the one or more precious metal salt precursor 106. Thesecond reaction results in the formation of precious metal NPs thatrapidly alloy with the remaining seeding NPs in the quantity of asolution of one or more precious metal salt precursor 106 to form themetal NAs. Accordingly, the aforementioned reaction pathways aresystematically driven by tuning the initial precious metal saltconcentrations and solution phase pH to synthesize metal NAs withcontrollable characteristics including, but not limited to, size, atomicratio and alloying degrees.

FIG. 2 illustrates a flow diagram of a method, generally designated 200,for producing a metal NA using tandem LASiS-GRR. In a first step 202,the method comprises disposing a first metal composition within areaction cell. For example, step 202 may comprise disposing anon-precious, transition metal as a solid metal target 104 for ablationwithin the reaction cell 102 as illustrated in FIG. 1.

In a second step 204, the method comprises adding a quantity of a secondmetal composition into the reaction cell. For example, step 204 maycomprise injecting into the reaction cell 102 a quantity of a solutionof one or more precious metal salt precursor 106 chosen to bear a higherredox potential than the non-precious, transition metal target 104.

In a third step 206, the method comprises ablating, with a laser, thefirst metal composition disposed in the quantity of the second metalcomposition within the reaction cell. For example, step 206 may compriseablating with a laser 110 the non-precious, transition metal target 104disposed in the quantity of a solution of one or more precious metalsalt precursor 106 inside the reaction cell 102, while the non-precious,transition metal target 104 is continuously rotated for uniformlyablation. In some aspects, the non-precious, transition metal target 104may be configured to be rotated by a motor 112, as illustrated in FIG.1.

In a fourth step 208, the method comprises tuning one or more reactionparameter and/or one or more functional parameter during the tandemLASiS-GRR in order to tailor at least one characteristic of the metal NAand/or the metal NC. For example, step 208 may comprise tuning one ormore laser parameter comprising laser energy (fluence) betweenapproximately, e.g., 0.5-500 J/cm², including but not limited to 1, 5,10, 50, 60, 100, 200, 250, 300, 400, or 500 J/cm², laser wavelengthusing for example, a 532 or 1064 nm laser, and a period of time thelaser is configured to ablate the first metal composition; environmentalparameters comprising an initial quantity of a solution of the secondmetal composition in the reaction cell, and a solution phase pHcondition, such as but not limited to a pH between approximately 0 to14, including but not limited to a pH of about 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13 or 14; and/or a functional parameter comprisingsimultaneous ultra-sonication for dispersing ablated species, controlledchemical injection of the second metal composition or other chemicalagents, rotation of the first metal composition for uniform ablation,and controlled temperature and environmental gas (e.g., N₂, O₂, etc.)for the reaction cell in order to tailor at least one of a size, ashape, a structure, and/or a composition of the metal NA and/or themetal NC.

In some embodiments, the presently disclosed subject matter relates tocompositions including at least metal heteronanostructures, a term broadenough to encompass both a metal NA and a metal NC. In some embodiments,a metal heteronanostructure in accordance with the presently disclosedsubject matter comprises a first metal and at least a second metal. Insome embodiments, the metal heteronanostructure is produced using tandemLASiS-GRR. In some embodiments, the metal heteronanostructure is stableunder acidic and/or alkaline conditions. In some embodiments, a metalheteronanostructure in accordance with the presently disclosed subjectmatter is a nanomaterial.

In some embodiments, a metal heteronanostructure in accordance with thepresently disclosed subject matter has at least one characteristicconfigured to be tailored during the tandem LASiS-GRR by tuning one ormore reaction parameter and/or one or more functional parameter duringthe tandem LASiS-GRR. In some embodiments, the at least onecharacteristic comprises a size, a shape, a structure, and/or acomposition of the metal composition.

In some embodiments, the metal composition can comprise nano-sizedparticles that are approximately spherical. When the nano-sized particleis approximately spherical, the characteristic dimension can correspondto the diameter of the sphere. In addition to spherical shapes, thenanomaterial can be disc-shaped, plate-shaped (e.g., hexagonallyplate-like), oblong, polyhedral, rod-shaped, cubic, orirregularly-shaped.

In some embodiments, the tailoring of the composition comprises aparticular degree of metal alloying, such as but not limited to 40-60%.As illustrated in the Examples provided herein below, for particularspecific PtCo NA compositions, the products have spherical shapes, withmean size ranging from 3-18 nm, and the degree of alloying ranging from40-60%. By rationally tailoring of these compositions, theelectrocatalytic activity of the NAs may then be optimized.

In some embodiments, the tailoring of the composition comprisesproviding a mean crystallite size, which can be estimated from XRD data.In some embodiments, the mean crystallite size ranges from about 1 to 20nm. In some embodiments, the mean crystallite size is about 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nm. Forparticular PtCo NA compositions, by rationally tailoring of the meancrystallite size, the electrocatalytic activity of the NAs may then beoptimized.

In some embodiments, the first metal used as the target for tandemLASiS-GRR bears a lower redox potential than the redox potential of thesecond metal, such as a second metal used in the form of salt precursorsolution. In some embodiments, the seeding metal NPs generated fromLASiS on the first metal target get oxidized, while reducing the secondmetal salt precursor in turn during the GRR. In some embodiments of ametal heteronanostructure of the presently disclosed subject matter, thefirst metal comprises a non-precious, transition metal and the at leastone second metal comprises at least one precious metal having a higherredox potential than the non-precious, transition metal. Notably, wherethe first metal comprises a metal other than a non-precious, transitionmetal and the at least one second metal comprises a metal other than atleast one precious metal, tandem LASiS-GRR may still synthesize an NCand/or an NA as long as the second metal comprises a higher redoxpotential than the first metal.

Any precious metal or transition metal as would be apparent to one ofordinary skill in the art upon a review of the instant disclosurecomprise can be employed in accordance with the presently disclosedsubject matter. Representative precious metals include but are notlimited to platinum (Pt), gold (Au), silver (Ag), copper (Cu), palladium(Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os).

A representative non-precious transition metal is a 3-d transitionmetal. Thus, representative transition metals can include, for example,scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese(Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn).In some embodiments, the transition metal can be any element with apartially filled d sub-shell or which can form a cation with a partiallyfilled d sub-shell. In some embodiments, the transition metal can be anyelement from the d-or f-block of the Periodic Table. Thus, in someembodiments the transition metal can be selected from Sc, Ti, V, Cr, Mn,Fe, Co, Ni, Cu, Zn, yttrium (Y), zirconium (Zr), niobium (Nb),molybdenum (Mo), technium (Tc), ruthenium (Ru), rhodium (Rh), palladium(Pd), silver (Ag), cadmium (Cd), lutetium (Lu), hafnium (Hf), tantalum(Ta), tungsten (W), rhenium (Rd), osmium (Os), iridium (Ir), platinum(Pt), gold (Au), rutherfordium (Rf), dubnium (Db), seaborgium (Sg),bohrium (Bh), hassium (Hs), copernicium (Cn), elements in the actinideseries (i.e., actinium (Ac), thorium (Th), protactinium (Pa), uranium(U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm),berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm),mendelevium (Md), nobelium (No), and lawrencium (Lr)) and elements inthe lanthanide series (i.e., cerium (Ce), dysprosium (Dy), erbium (Er),europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium(Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm),terbium (Tb), thulium (Tm), and ytterbium (Yb)). In some embodiments,the transition metal is a non-precious transition metal such as, but notlimited to, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, Tc, Lu, Hf,Ta, W, Rd, Rf, Db, Sg, Bh, Hs, Cn, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk,Cf, Es, Fm, Md, No, Lr, Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Pm, Sm,Tb, Tm, and Yb.

The metal heteronanostructure can comprise a core region (i.e., thespace between the outer dimensions of a particle of the composition) anda shell or matrix (i.e., a surface that defines the outer dimensions ofa particle of the composition). In some embodiments, a metalheteronanostructure in accordance with the presently disclosed subjectmatter comprises a substantially uniform alloyed core of a first metaland at least one second metal; and a shell or matrix surrounding thesubstantially uniform alloyed core, the shell or matrix comprising oneof the first metal and the at least one second metal. In someembodiments, a substantially uniform alloyed core comprises a uniformfirst metal to at least one second metal ratio. For example, a ratioranging from 0-38% may be provided.

In still further embodiments, a substantially uniform nanoalloy isprovided herein. The metal nanoalloy may comprise a first metal and atleast one second metal. In some embodiments, the first metal is aprecious metal and the second metal is a non-precious, transition metal.In some embodiments, a degree of alloying is approximately between40-60%, such as about 40, 42, 44, 46, 48, 50, 52, 54, 56, 58 and 60%.

In some embodiments, a nanocomposite and/or nanoalloy of the presentlydisclosed subject matter further comprises a third metal. In someembodiments, the substantially uniform alloyed core comprises the firstmetal, the second metal, and the third metal; and the shell or matrixsurrounding the substantially uniform alloyed core comprises one or moreof the first metal, the second metal, and the third metal. In someembodiments, the third metal has a higher redox potential than the firstmetal, the second metal, or both the first metal and the second metal.In some embodiments, both the second and the third metal formed from thereduction of metal salt precursors have higher redox potential than thefirst metal. For example, for PtCuCo NA, the redox potential for therespective first, second and third metals are Co²⁺/Co=−0.28 V,[PtCl₄]²⁻/Pt=0.755 V, Cu⁺/Cu=0.52 V. In some embodiments, a degree ofalloying among the first, second, third or more metal is approximatelybetween 40-60%, such as about 40, 42, 44, 46, 48, 50, 52, 54, 56, 58 and60%.

As used herein “substantially uniform” can refer to an alloy wherein theelement distribution is generally uniform for each individual alloyparticle and/or throughout each particle (e.g., the second metal isuniformly distributed throughout a solid composition of the firstmetal). In some embodiments, the ratio of metals remains substantiallythe same throughout an alloy particle. In some embodiments, thepercentage of non-precious transition metal varies only by about ±10%,±9%, ±8%, ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, ±1% or less between any twopoints in a solid particle (e.g., a nanoparticle) comprising the alloyor between any two particles of the alloy. For example, when thepercentage of non-precious transition metal varies only by about ±5%between any two points in an alloy particle, one region of the particlecan comprise about 10% of the non-precious transition metal and about90% of the precious metal, while another region of the particle cancomprise about 15% of the non-precious transition metal and about 85% ofthe precious metal.

Alternatively, in some embodiments, “substantially uniform” can refer tothe alloy particles all comprise approximately the same shape or havingthe same size (e.g., where the largest diameter of any alloy particle ina mixture of particles varies only by about 20, 15, 10, 9, 8, 7, 6, 5,4, 3, 2, or 1 nm from the largest diameter of any other particle in themixture).

In some embodiments, the shell or matrix comprises an oxide of one ofthe first metal and the at least one second metal such that the metalheteronanostructure is a metal nanocomposite. In some embodiments, theshell or matrix surrounding the substantially uniform alloyed corecomprises the precious metal or the non-precious, transition metal. Insome embodiments, the substantially uniform alloyed core comprises auniform precious metal to at least one non-precious, transition metalratio, with the ratio ranging from 0-38%. Accordingly, the metalheteronanostructure may be formed from a precious metal that is reduced20-40% as compared to a known composition comprising a precious metal,such as a known catalyst composition, which can provide a significantcost savings. For example, the metal heteronanostructure may comprisePtCo having a 20-40% reduction in Pt as compared to a known compositioncomprising Pt, such as a known Pt catalyst composition.

In some embodiments, the metal heteronanostructure is a metal NA thatcomprises a crystal structure having shrinkage in the lattice spacing,thereby indicating the alloy formation of two or more metals, and notthe parent metals segregated. By way of elaboration and not limitation,the presently disclosed subject matter can comprise formation of binaryand/or ternary NAs whose crystal structure indicates shrunken latticespacing as compared to the lattice spacing for the parent metals,thereby establishing that the NAs formed do not comprise segregatedintermetallic or pure metallic components. For instance, in the Examplespresented herein below, a PtCo NA comprises lattice constant thatshrinks from 3.92 Å (for pure Pt) to 3.83 Å (with 38% Co). Thus, in someembodiments, a metal NA or a metal NC in accordance with the presentlydisclosed subject matter can comprise a shrinkage in lattice constantranging from approximately between 0 to 2.4%, including but not limitedto about 0.4, 0.8, 1.2, 1.6, 2.0 or 2.4% shrinkage in lattice constant.

In some embodiments, a metal heteronanostructure of the presentlydisclosed subject matter is a binary NA that may be produced from thetandem LASiS-GRR disclosed herein and includes, but is not limited to,PtCo, PtNi, PtCu, and PdCo, while a ternary NA that may be produced fromthe tandem LASiS-GRR disclosed herein includes, but is not limited to,PtCuCo, PtCoMn, and PtCoNi. Likewise, a binary NC may be produced bytandem LASiS-GRR and includes an NA embedded in a nanomatrix. Forexample, an NA of PtCo may be embedded in CoOx to provide a binary metalNC of PtCo/CoOx, which provides for the synergic “spill-over effect”that accelerate both ORR and OER on the preferred phases, i.e., ORR onPtCo NA and OER on CoOx through symbiotic, site-specificadsorption/desorption of intermediate species, while preventingaggregation and/or dissolution of the NA in alkaline medium. Moreparticularly, while it is not desired to be bound by any particulartheory of operation, it appears that each of the sites provides refugefor the undesirable species from the other sites, thereby promoting boththe reactions. A binary metal NC, such as PtCo/CoOx, may exhibitimproved bifunctional catalytic properties, which may be attributed tothe unique heteronanostructuring of alloyed PtCo NPs embedded in thesponge-shaped CoO_(x) matrices which, while contributing to the enhancedORR and OER behaviors due to the synergic “spillover” effects, preventthe PtCo NPs from aggregation and dissolution in the alkaline media.Additional binary NCs that may be produced from the tandem LASiS-GRRdisclosed herein include, but are not limited to, PdCo/CoOx, Ag/ZnO, andAg/TiOx.

EXPERIMENTAL RESULTS

A Zeiss Libra 200MC monochromated transmission electron microscope (TEM)was used with an accelerating voltage of 200 kV for regular TEMcharacterizations along with selected area electron diffraction (SAED)and high resolution transmission electron microscopy (HRTEM) imaging.Large-scale and small-scale elemental mappings are obtained from energydispersive X-ray spectroscopy (EDX) and electron energy-lossspectroscopy (EELS) analysis. In-formation limitation of HRTEM image is0.1 nm. Spatial resolution of the STEM image is approximately 0.4 nm.Resolution of EELS spectrum with monochromator is 0.1 eV measured atfull width of half maximum (FWHM) of zero-loss peak in the vacuum.Inductively coupled plasma optical emission spectroscopy (ICP-OES)obtained from Perkin Elmer, OPTIMA 4300™ DV was used to measure theconcentration for both Pt and Co nanoparticles (NPs). Standard cobaltdichloride solution (≧99%) and K₂PtCl₄ solution (>99.9%) were used forcalibration. X-ray diffraction (XRD) was carried out on a PhillipsX'Pert-Pro diffractometer equipped with a Cu Ka source at 40 kV and 20mA. The mean crystal sizes of the NAs were calculated according toScherrer equation:

$\begin{matrix}{d = \frac{0.9\lambda}{\beta \; \cos \; \theta}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where d is the mean crystal size, λ is wavelength of the X-ray, β is theline broadening at FWHM, θ is the Bragg angle.

The Co atomic fractions in the alloy (x) were evaluated using theVegard's law,

$\begin{matrix}{x = {\left\lfloor \frac{a - a_{0}}{a_{s} - a_{0}} \right\rfloor \cdot x_{s}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

where a_(O) and a_(S) are the lattice parameters of Pt (0.393 nm) andPt₃Co (0.383 nm), and x_(S) is the Co atomic fraction (0.25) in thePt₃Co catalyst. The degree of alloy, i.e., the alloyed Co(Co_(al)) tototal Co in the catalyst (Co_(tot)) ratio can then be expressed by:

$\begin{matrix}{\frac{{Co}_{al}}{{Co}_{tot}} = \frac{{xPt}_{ICP}}{\left( {1 - x} \right){Co}_{ICP}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where Pt_(ICP) and Co_(ICP) are the integral atomic ratios of Pt and Cofrom ICP-OES measurements, respectively.

In some aspects, a rotating disk electrode (RDE) setup was bought fromPine instrument company, LLC. A conventional, three-compartmentelectrochemical cell comprising of a saturated double junction Ag/AgClelectrode as the reference electrode, a glassy carbon RDE with diameterof 5 mm as the working electrode, and a platinum coil as the counterelectrode were used. Slightly different setups were used for testing ORRand/or OER activities for NCs and NAs.

In some aspects, for testing bifunctional ORR and/or OER activities ofNCs, all electrochemistry (EC) tests were carried out at roomtemperature in 1.0 M KOH solution with the reference electrodecalibrated in response to the RHE. 30% Pt/C from BASF was used as thestandard catalyst for comparison. For ORR tests, synthesized NPs werefirst mixed with Vulcan XC-72 carbon black (CB) powder (particle sizebetween approximately 20-40 nm, procured from Cabot Company) in aqueoussolution with a weight ratio of 1:4 (NP: CB). After 2 hours ofultrasonication, the slurry was stirred for 24 hours and then completelydried in a vacuum at approximately 80° C. Thereafter, the catalyst inkwas prepared by suspending 2 mg of the dried mixture in 0.5 mL methanoland 25 μl of 5 wt % Nafion solution (Sigma-Aldrich, density 0.874 g/mL)via 30 mins of ultrasonication. For preparing the working electrode, 6μL of the prepared catalyst ink was coated on the RDE where the NPloading density was calculated to be 24.5 μg/cm². As for the OER tests,synthesized NPs were deposited on the GCE directly by vacuum drying atroom temperature, with a deposition density calculated as 2 μg/cm² forall the catalysts. Linear sweep voltammogram (LSV) for ORR and OER wereconducted on the RDE set-up by sweeping the potential from +0.3 to +1.1V (ORR) and +1.1 to +1.7 V (OER) respectively.

In some aspects, for testing ORR activities for the NAs, 0.1 M HClO₄solution was used as electrolyte, 20% Pt/C from BASF was used as thestandard catalyst for comparison. Synthesized NPs were first mixed withVulcan XC-72 CB powder (particle size approximately between 20-40 nm,procured from Cabot Company) in aqueous solution with a weight ratio of1:3 (NP: CB). After 2 hours of ultrasonication, the slurry was stirredfor 24 hours and then, completely dried in vacuum at 80° C. Thereafter,the catalyst ink was prepared by suspending 2 mg of the dried mixture in1 mL ethanol and 5 μl of 5 wt % Nafion™ solution (Sigma-Aldrich, density0.874 g/mL) via 30 min of ultrasonication. For preparing the workingelectrode, rotational drying method was applied wherein, 10 μL of theprepared catalyst ink was casted on the surface of the glassy carbonelectrode (GCE) that was inversely placed on the RDE setup and rotatedat 700 rpm for 5 min. The NP loading density was calculated to be 25μg/cm². Cyclic voltammetry was conducted over a potential range from+0.05 V to +1.00 V at a scan rate of 50 mV/s after pre-scan the samepotential range at 100 mV/s for 50 cycles. The ORR polarization curveswere obtained by sweeping the potential from +0.05 to +1.02 V at a scanrate of 5 mV/s and a rotation rate of 1600 rpm. The dynamics of theelectron transfer process in ORR were analyzed through the rotating diskvoltammetry (RDV) at different speeds (ranging between 400 and 2200 rpm)based on the Koutecky-Levich (KL) equation:

$\begin{matrix}{\frac{1}{J} = {{\frac{1}{J_{K}} + \frac{1}{J_{L}}} = {\frac{1}{J_{K}} + \frac{1}{B\; \omega^{1/2}}}}} & {{Equation}\mspace{14mu} 4} \\{{J_{K} = {nFkC}_{0}};{B = {0.62{nFC}_{0}D_{0}^{2/3}v^{{- 1}/6}}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

where J, J_(K) and J_(L) are the measured, kinetic, and diffusionlimiting current densities, respectively, n is the electron transfernumber, F is the Faraday constant (96 485 C*mol⁻¹), Co and Do are thedissolved O₂ concentration the O₂ and the diffusion coefficient in theelectrolyte respectively, n is the electrode rotation rate in rpm. Tafelplots are generated using the kinetic current J_(K) as determined from:

$\begin{matrix}{J_{K} = \frac{J \cdot J_{L}}{J_{L} - J}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

The electrochemical surface area (ECSA) was determined by the hydrogendesorption area in the CV curve between 0.05 and 0.4 V vs. RHE based onthe following equation:

$\begin{matrix}{{ECSA} = \frac{Q_{H}}{m \times q_{H}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

where Q_(H) is the charge for hydrogen desorption, m is the loadingamount of metal in the electrode, and q_(H) is the charge required formonolayer desorption of hydrogen on Pt (210 μC/cm²).

Example 1—Synthesis of Binary Nanoalloys 1.1—Different Pt SaltConcentrations

The PtCo NA samples of PtCo-1, PtCo-2, PtCo-3, and PtCo-4, assynthesized by LASiS-GRR for various K₂PtCl₄ concentrations and ablationtimes are depicted in the TEM images in FIGS. 3A-3D along with thecorresponding SAED patterns (inset). Notably, the scale bar in the SAEDpatterns is 5 (1/nm).

FIG. 3A illustrates PtCo-1 synthesized at a K₂PtCl₄ concentration of 125mg/l with a respective ablation time of 4 minutes. FIG. 3B illustratesPtCo-2 synthesized at a K₂PtCl₄ concentration of 250 mg/l with arespective ablation time of 7 minutes. FIG. 3C illustrates PtCo-3synthesized at a K₂PtCl₄ concentration of 375 mg/l with a respectiveablation time of 13 minutes. FIG. 3D illustrates PtCo-4 synthesized at aK₂PtCl₄ concentration of 500 mg/l with a respective ablation time of 20minutes.

In some aspects, experiments were performed using differentlysynthesized NA samples of PtCo-1, PtCo-2, PtCo-3, and PtCo-4. In each ofthe differently synthesized NA samples, it was determined that theinitial products from the LASiS-GRR synthesis were found to be alloyedPtCo NPs embedded in sponge shaped CoO_(x) matrices. In some aspects,post-treatment of the as-synthesized PtCo/CoO_(x) NC suspensions withHCl acid solutions at pH2 for 20 hours led to the complete removal ofall CoO_(x) matrices leaving behind the pure spherical PtCo NAs. Thesespherical PtCo NAs are found to exhibit clean PtCo characteristicdiffraction rings as seen from SAED patterns in FIGS. 5A-H. Theparticles are largely found to be spherical due to the surface atomreconstruction induced by laser irradiation [57]. TEM images in FIGS.3A-3D also illustrate a systematic increase in the average particlesizes between the samples PtCo-1 and PtCo-4. Detailed mean crystallitesizes, as estimated from XRD data, are found to be approximately 3.16,4.7, 9.00 and 10.06 nm for PtCo-1, PtCo-2, PtCo-3, and PtCo-4 samples,respectively (Table 1).

TABLE 1 Degree of K₂PtCl₄ Co ratio % Crystallite alloying C (mg/l)(ICP-OES) 2θ (111) size (nm) a (Å) x (%) pH 3 250 6.4 39.81 17.98 3.9190.03 44.77 pH 7 125 20.6 40.2 3.16 3.882 0.12 53.33 250 22.1 40.29 4.73.874 0.14 58.01 375 19.9 40.13 9 3.889 0.1 46.57 500 15.5 40.05 10.063.896 0.09 51.7 pH 11 250 38.1 40.85 4.15 3.828 0.26 55.96

FIG. 4 illustrates a comparison of XRD patterns for various PtCo NAssynthesized at different initial K₂PtCl₄ concentrations and ablationtimes. Notably, the black dashed lines in FIG. 4 mark the standard peakpositions for the respective labeled species. Mean crystallite sizes arecalculated from the FWHM of the PtCo (111) peaks in the XRD patterns byapplying the Scherrer equation (Equation 1). The augmentation of meanparticle sizes with higher initial [Pt²⁺] is due to the larger degree ofcoalescence and/or Ostwald ripening among the seeding PtCo NPs due tofaster reduction rates of the K₂PtCl₄ salt by the seeding Co NPs [56].The alloying of Co into Pt is demonstrated by the clear shift of PtCocharacteristic peaks to higher angles in the XRD patterns in FIG. 4,when compared to the corresponding 2θ values for pure Pt peaks.Specifically, the Pt (111) peak shifts from 39.8° for pure Pt to 40.20°,40.29°, 40.13°, and 40.05° for PtCo-1, PtCo-2, PtCo-3 and PtCo-4 NAs,respectively, is in accordance with the evolution of Co atomic ratios(%) of 20.6, 22.1, 19.9, and 15.5 in the respective alloys, ascalculated from ICP-OES measurements (shown in Table 1). Table 1 alsosummarizes the values of Co atomic fractions in the alloys (x) and theratio of alloyed Co (forming Pt₃Co) to total Co (Co_(al)/Co_(tot)), ascalculated from Vegard's law (Equation 2) and ICP-OES measurement(Equation 3). These calculations reveal the alloying degrees to varyfrom approximately 44% to approximately 58% for the aforementionedrespective PtCo NAs synthesized. Notably, it was found duringexperimentation that surface facets of a specific PtCo-2 particle aredominated by the PtCo (111) that is well-known for its lower oxygenbinding energy and hence, higher ORR activity [30, 58, 59].

In an effort to further investigate the elemental distributions withinthe NAs from large-scale as well as detailed elemental mappingsrespectively, EDX and EELS measurements for the PtCo-2 sample areillustrated in FIGS. 5A-5H. The EDX mapping results in FIGS. 5A-5Cillustrate that both Pt and Co are uniformly distributed in all the NPs.FIG. 5D illustrates a representative EELS spectrum taken from a singleNP (shown in the inset), where the two groups of peaks with onsetslocated at approximately 519 and 779 eV are ascribed to the Pt—N_(2,3)and the Co-L_(2,3) edges respectively. The corresponding Pt and Co EELSmapping for this particle are exhibited in FIGS. 5E-5F, where the Ptdistribution area (FIG. 5E) is found to be slightly larger than that forCo (FIG. 5F). For better comparison, the Pt:Co ratio mapping along witha representative line scan across the particle is shown in FIG. 5G, andthe corresponding Pt atomic (%) distribution across this line scan isshown in FIG. 5H. These results reveal a thin Pt-rich layer (i.e., a fewnanometers) as the particle shell wherein the Co (%) increases graduallytowards inner layers. In contrast, the center of the NP bears arelatively uniform but lower Pt:Co ratio (e.g., Pt:Co is approximately4.5:1). Here it needs to be mentioned that in spite of the higheraccuracy of the EELS technique, the inclusion of other signals (e.g.,O-K edge at 532 eV) and random noises in the broad Pt—N_(2,3) peak fromEELS data can contribute to the slightly higher value of the Pt:Coratios as calculated from EELS measurements, when compared to that fromEDX/ICP-OES quantifications.

1.2—Different pH Conditions

For investigating the impact of the solution phase [H⁺] on the structureand composition of the resultant NAs, similar experiments were carriedout at pH3 and pH11 conditions respectively (with initial [K₂PtCl₄] of250 mg/l, and ablation time of 7 min) followed by HCl treatment at pH2conditions. The PtCo NAs synthesized at pH3 show a much larger meancrystallite size (e.g., approximately 17.98 nm) as compared to those atpH11 condition (e.g., approximately 4.15 nm). The EDX mappings andspectra also indicate that Co molar ratio in the NA products rises upwith the solution phase pH (namely from pH3, pH7, pH11), as discussed indetails in the supporting information along with corresponding TEMimages in Table 1. It needs to be mentioned that under pH11 conditions,the Pt²⁺ gets reduced to Pt(OH)₂ that eventually precipitates as PtCl₂thereby reducing both Pt formation and agglomeration. In this case,addition of saturated NaCl solution followed by centrifugation for twotimes helped remove the unwanted PtCl₂ salts. The ICP-OES results alsosupport the EDX data wherein the three Co molar ratios for pH3, pH7 andpH11 cases are found to be 6.4%, 22.1% and 38.1% respectively (Table 1).Furthermore, FIG. 6 illustrates XRD patterns for PtCo NAs at differentpH conditions with same initial K₂PtCl₄ concentration and ablation time(250 mg/l and 7 min), where the dash lines mark the standard peakpositions for each species. In FIG. 6, the XRD profiles indicatenegligible shift in 28 value(39.81°) for the characteristic PtCo (111)peak in the pH3 sample as compared to the remarkable positiveshift(40.85°) in 28 values for the PtCo alloy formed at pH11, which ismuch higher than those for the PtCo-2 sample(40.29°) as well as forstandard Pt₃Co(40.53°) alloys. In such a case Pt₁Co₁ alloy(41.4°) withtetragonal crystalline structure might have been partially formed. Theaforementioned results for different and yet, directed alloying underdifferent pH conditions are achieved by controlling the relativeconcentrations of Pt²⁺, Co and H⁺ in the system. Specifically, in acidcondition, majority of the Co NPs undergo direct oxidation by solutionphase [H⁺], which results in fewer amounts of Co available for Pt²⁺reduction and even less available for alloying with Pt. Conversely, atpH11 condition, direct oxidation of Co is to a great extent hindered dueto the extremely low [H⁺] in solution. As a consequence, large amount ofCo take part in GRR with Pt²⁺ and in turn alloying with Pt, therebyleading to a much higher Co_(al) in the final products.

The ORR catalytic activities for the PtCo NAs synthesized with variousinitial [Pt²⁺], as investigated with RDE measurements in 0.1 M HClO₄electrolyte solutions, are summarized in FIGS. 7A-7F. Cyclic voltammetry(CV) scans were conducted from 0.05 to 1.02 V vs. RHE at a scan rate of50 mV/s. The ECSA calculated from the integration of the hydrogenevolution area in the CV curve indicate a gradual decrease from PtCo-1to PtCo-4 (i.e., 30.92, 24.25, 18.31 and 14.55 m²/g respectively), asshown in FIG. 7A and Table 1. This is mainly attributed to thedecreasing surface to volume ratios with increasing particle sizes ofthe PtCo NAs resulting from LASiS-GRR with higher initial [Pt²⁺]. FIG.7B illustrates linear sweep voltammograms for the ORR polarizationcurves scanned in O₂-saturated 0.1 M HClO₄ electrolyte for the PtCocatalysts under study. The half-wave potential values in FIG. 7Bindicate that most of the as-synthesized NA samples, i.e., PtCo-1,PtCo-2 and PtCo-3, outperform the catalytic activities of commercialPt/C. The best ORR performance is noted for PtCo-2 sample with a 32 mVpositive shift in the half-wave potential as compared to the Pt/Csample. This is mainly due to higher Co ratios with good alloying degree(58.01%) in the PtCo-2 sample that shrinks the lattice constant andlowers d-band center which in turn reduces the oxygen binding energy.Added to this, the small particle sizes (mean crystallite size of 4.7 nmin Table 1) with moderate coalescence in PtCo-2 promote catalyticactivities due to higher surface to volume ratios. In contrast, thePtCo-4 alloy exhibits the lowest activity, which can be ascribed to itslowest Co ratio (15.5%), poor alloying (51.7%) and largest size(approximately 10 nm) as seen from Table 1. Interestingly, the PtCo-1sample with smallest mean sizes (approximately 3 nm) and slightly loweralloying degree (53.33%) than PtCo-2 (58%), exhibits less activity. Thiscould be primarily attributed to the excess agglomeration in PtCo-1 (seeFIG. 5A). Besides, the diffusion-limited current at high overpotentialregions (+0.1 to +0.80 V vs. RHE) reaches approximately 5.6 mA/cm² forall samples, thereby indicating minimal formation of H₂O₂ during the ORRprocess as well as good charge transfer rates. It is noted that thisdiffusion-limited current value agrees extremely well with thosereported for commercial Pt/C and other peer research works [16, 60]. Thedynamics of the electron transfer process during ORR were analyzed usingthe KL equation in rotating disk voltammetry (RDV) measurements carriedout at different rotation rates (400 to 2200 rpm), as indicated in theexperimental section.

FIG. 7C illustrates the slopes of the KL plots generated from the RDVcurves (inset) for the PtCo-2 at different potentials in the range of0.70-0.87 V. The slopes estimate the number of transferred electrons (n)to be approximately 4.0, thereby indicating an ideal four-electrontransport process for ORR. FIG. 7D illustrates the Tafel plots extractedfrom the ORR polarization curves in the mixed kinetic and/or diffusionregions (low overpotential regions). The calculated Tafel slopes for thePtCo samples are in the range from 56.4 to 67.4 mV/dec, which are lowerthan the corresponding values for commercial Pt/C (70.5 mV/dec),indicating better charge carrier mobility. Besides, upon comparing thespecific activities (SA) for each of the samples at 0.9 V vs. RHEpotential on the Tafel plots in FIG. 7D, all the PtCo samples are foundto indicate higher SA values than the Pt/C sample. The detailed massactivity (MA) and SA values at 0.9 V vs. RHE are shown in FIG. 7E andTable 1. The PtCo-2 sample is found to indicate the best catalyticactivity with the MA and SA values of 0.28 mA/μg_(Pt) and 1.18 mA/cm²,respectively, thereby indicating about a three and six-fold increaseover the corresponding values for Pt/C (0.09 mA/μg_(Pt) and 0.19mA/cm²). The outstanding ORR activities for the PtCo NAs is attributedto the uniform NAs with the Pt-rich shell, as evident from the EELSratio mapping in FIGS. 5G-H. Added to this, the absence of anyadditional chemical including reducing agent/surfactant/stabilizationagent during the LASiS-GRR synthesis process eliminates thepossibilities of deteriorating the active surface area, therebybenefiting the catalytic performance. Finally, stability tests wereconducted for the PtCo-2 sample by scanning CV at the same range asearlier CV tests for 5000 cycles at 100 mV/s. The results shown in FIG.7F reveal an approximately 14% decrease in ECSA (from 100% (black) to86.2% (green) case) after 5000 cycles, while the Co_(al) also diminishesfrom 22.1% to 18.3%. This is ascribed to the dissolution of catalysts inthe acid electrolyte, which is a well-known phenomenon for Pt or othermetal based ORR catalysts as also observed in earlier works[4,11,22,30].

The electrochemistry results for the PtCo NAs synthesized at differentpH conditions (referred to as pH3, pH7 and pH11 samples) are summarizedin FIGS. 8A-D. The pH11 sample exhibits a much higher ECSA (44.50 m²/g)than the pH7 or PtCo-2 (24.25 m²/g) and pH3 sample (6.67 m²/g) ascalculated from the hydrogen adsorption peaks in the CV curves (FIG.8A). This is easily attributed to the smaller crystallite sizes(approximately 4.15 nm from Table 1) for the pH11 sample as compared toboth the pH7 (approximately 4.70 nm) and pH3 (approximately 17.98 nm)samples. For comparing the ORR activities, electrochemistry tests andplots similar to the ones carried out for PtCo-2 samples at pH7condition are presented in FIGS. 8A-D. These measurements include ORRpolarization curves (FIG. 8B), Tafel plots (FIG. 8C), and MA/SAcomparisons (FIG. 8D). The pH3 sample exhibits the poorest activity ascompared to all the other samples, which can be ascribed to its largercrystallite sizes and extremely low Co_(al) (see Table 1). Here theinteresting observation is that the pH11 sample, even with higherCo_(al) (approximately 38.1%) and smaller crystallite sizes(approximately 4.15 nm), exhibit slightly less ORR activities in regardsto the half-wave potential (approximately 875 V vs. RHE), MA(approximately 0.24 A/mg), and SA (approximately 0.53 mA/cm²) whencompare to the corresponding values for PtCo-2 (namely, 899 V vs. RHE,0.28 A/mg and 1.18 mA/cm²). Nevertheless, it needs to be noted thatthese values are still remarkably better than those for commercial Pt/C(namely, 867 V vs. RHE, 0.09 A/mg and 0.19 mA/cm², respectively).

FIG. 9 illustrates a schematic of a system, generally designated 900,similar to system 100 illustrated in FIG. 1, that is configured tosynthesize PtCo NAs via tandem LASiS-GRR using different initial Pt²⁺concentrations and pH conditions. In system 900, a metal target 902 isablated by a laser 904 to produce seeding Co NPs which expand with acavitation bubble 906 and react with either Pt²⁺, H⁺, or reduced Pt(alloying process) at a bubble-liquid interface 908 during collisionalquenching. Based on the different Pt²⁺ concentration (low, medium, high)and pH conditions (acid, neutral, alkaline), different degrees ofalloying for Co_(al) may be obtained. The formation of PtCo NAs mayoccur in a reaction cell (e.g., 102, FIG. 1) using a pulsed lasersimilar to that which is illustrated in FIG. 1. In an O₂-free solution,the laser (e.g., an Nd: YAG pulsed laser) 904 produces seeding metal NPswithin the cavitation bubble 906 that undergo reactions. For example,the following reactions at the bubble-liquid interface 908 may occurduring collisional quenching:

-   1. Galvanic replacement reaction (GRR) with K₂PtCl₄ based on the    respective redox potentials for Co/Co²⁺(−0.28 V vs. SHE) and.    [PtCl₄]²⁻/Pt (0.755 V vs. SHE):

[PtCl₄]²⁻+Co=Pt+Co²⁺  Reaction 1

-   2. Oxidation by H⁺ ions driven by pH:

Co+2H⁺=Co²⁺+H₂  Reaction 2

-   3. Alloying with reduced Pt from Reaction 1:

Co+Pt=PtCo(alloy)  Reaction 3

At neutral conditions (pH=7), with same Co production rate from the ratelimiting steps of LASiS, the initial [PtCl₄]²⁻ plays a crucial role indriving the rate determining steps of Reactions 1 through 3 to finallycontrol the nanostructures and compositions. Specifically, when theinitial [PtCl₄]²⁻ is low, the reduction rate of Pt through GRR(Reaction 1) is much slower than the direct oxidation of Co by H⁺(Reaction 2), therefore the alloying rate between reduced Pt and Co(Reaction 3) is also slow. Conversely, high initial [PtCl₄]²⁻ leads to amuch faster Reaction 1 than the other two reactions, therefore leavingfew Co to alloy with large amount of reduced Pt and hindering thealloying process. To this end, an optimal amount of initial [PtCl₄]²⁻ isexpected to produce the largest alloyed Co (Co_(al)).

Meanwhile, the Pt—Co alloying process is also controlled by tuning thesolution phase [H⁺] or pH conditions. Specifically, in acid conditions(low pH), an extremely low Co_(al) is expected since majority of theseeding Co NPs go through Reaction 2 leaving few Co for Reaction 3,which is similar to the case with low [PtCl₄]²⁻ at neutral condition.Conversely, in alkaline conditions (high pH) with medium [PtCl₄]²⁻,abundant Co are present for Reaction 3, in which case the highestCo_(al) is obtained.

Consequently, the modified tandem LASiS-GRR technique is configured tosynthesize metal NAs and NCs with unique nanostructures as well as atleast one tailorable characteristic including sizes, Pt:Co ratios,and/or degrees of alloying. For example, the LASiS-GRR technique reportsNAs having crystallite sizes of approximately 4.70 nm and approximately58% degree of alloying (approximately 22% reduction in Pt atomiccontent) exhibit superior ORR activities in acid electrolyte solutionsas compared to the corresponding activities for standard Pt/C catalysts.Such activities are attributed to the unique capabilities of tandemLASiS-GRR to synthesize the aforementioned NAs with controlled sizes anduniform elemental distributions. Specifically, detailed structuralcharacterizations of the NAs from EDX and EELS ratio mappings indicate athin layer of Pt-rich shell on an alloyed core with relatively uniformPt:Co ratio. The rational tuning of such structure-property relationsare achieved by systematically controlling the reaction and functionalparameters (e.g., initial Pt salt concentrations, ablation times andsolution phase pH conditions) during tandem LASiS-GRR. Advantageously,the ability of seeding NPs generated by the rate limiting step of LASiSto drive the simple redox chemistry in the rate controlling step of GRRallows directed tailoring of sizes, structures, alloying, andcompositions in the final NCs and/or NAs. Accordingly, when operated intandem, reaction pathways emerging from high-energy liquid-confinedplasma can be regulated to create heteronanostructures with metastablestructures and phases without the use of any external chemicalagents/surfactants.

Example 2—Synthesis of Nanocomposites 2.1—PtCo/CoO_(x) Nanocomposites:Bifunctional Electrocatalysts ORR and OER

Four different NC colloidal samples of PtCo-5, PtCo-6, PtCo-7, andPtCo-8, each having a different initial K₂PtCl₄ concentration initiallyproduced through LASiS are depicted in TEM images in FIGS. 10A-10D. Forexample, FIG. 10A illustrates PtCo-5 synthesized at a K₂PtCl₄concentration of 25 mg/l. FIG. 10B illustrates PtCo-6 synthesized at aK₂PtCl₄ concentration of 60 mg/l. FIG. 10C illustrates PtCo-7synthesized at a K₂PtCl₄ concentration of 120 mg/l. FIG. 10D illustratesPtCo-8 synthesized at a K₂PtCl₄ concentration of 250 mg/l. Thecorresponding Pt and Co NP concentrations in each of the samples, asrevealed from ICP-OES measurements, are summarized in Table 2.

TABLE 2 Initial K₂PtCl₄ Conc. Pt Conc. Co Conc. Molar Pt/Co (mg/l)(mg/l) (mg/l) ratio PtCo-5 25 7.3 20 1:9 PtCo-6 60 19 23 1:4 PtCo-7 12042 25 1:2 PtCo-8 250 81 25 1:1

The results indicate that approximately 60-70% of the precursor Pt saltis transformed into Pt NPs upon ablation at 60 J/cm² fluence for 30 min.The Pt:Co molar ratios were calculated to be approximately between 1:9,1:4, 1:2 and 1:1 for PtCo-5 to PtCo-8, respectively. In some aspects,any unreacted residual K₂PtCl₄ as well as any excess KCl formed waswashed away during the centrifugation step. For example, two types ofexemplary nanostructures can be found in each of the samples; namelyindividual spherical NPs (darker contrast) embedded in a large amount ofhighly porous “sponge-shaped” nanostructures (lighter contrast). Thesestructures are expected to be CoO (lighter) and Pt and/or PtCointermetallic (darker) NPs respectively, where the different contrastsin the transmitted electron intensities are due to their different massto charge ratios.

In some aspects, FIGS. 10E-10H illustrate size distributions for thedarker spherical Pt-based NPs (which are later revealed to be PtCo NAs).For example, FIG. 10E illustrates that PtCo-5 comprises a mean size ofapproximately 8.5 nm with a Pt:Co atomic ratio of 1:9. FIG. 10Fillustrates that PtCo-6 comprises a mean size of approximately 10.8 nmwith a Pt:Co atomic ratio of 1:4. FIG. 10G illustrates that PtCo-7comprises a mean size of approximately 11.7 nm with a Pt:Co atomic ratioof 1:2. FIG. 10H illustrates that PtCo-8 comprises a mean size ofapproximately 17.7 nm with a Pt:Co atomic ratio of 1:1. Thus, FIGS.10E-10H illustrate that mean sizes of dark colored PtCo alloyed NPsincrease from approximately 8.5 nm to 17.7 nm with an increase of thePt:Co ratios for PtCo/CoO_(x) NCs synthesized by tandem LASiS-GRR. Thisis ascribed to an enhanced coalescence due to increased concentrationsof Pt NPs.

Notably, LASiS on Co in the presence of K₂PtCl₄ salt solution, whenexposed to the identical ageing process, results in both Co₃O₄ and CoOnanostructures coexisting in the final products, in contrast to what hasbeen previously known in the art that initially formed metastable CoOupon three days of ageing underwent complete oxidization into Co₃O₄ bythe solution phase O₂ and H⁺. This may be due to the highlynon-equilibrium processes where the seeding Co NPs emerging from thecavitation bubble undergo ultra-fast quenching and reactions with thesolution phase metal salt ions at the liquid front. Thus, duringablation in the aqueous solution with K₂PtCl₄ salts, a large portion ofCo is converted to CoO through GRR rather than direct oxidation. Therelatively higher stability of these CoO NPs could possibly be due tothis inherently different formation mechanism. As a result, it isdifficult for the CoO NPs to further get oxidized into Co₃O₄ or theoxidation rate is much slower.

In some aspects, FIGS. 11A-11D provide HRTEM images of the PtCo-5 samplewith corresponding positions (i.e., B-D) marked that indicate thelattice fringes. In FIG. 11A, the area marked ‘B’ corresponds to Pt(111) (d=2.26 Å) illustrated in FIG. 11B, the area marked ‘C’corresponds to Co₃O₄ (220) (d=2.86 Å) illustrated in FIG. 11C, and thearea marked ‘D’ corresponds to CoO (200) (d=2.13 Å) illustrated in FIG.11D. Lastly, control experiments were also carried out for laserirradiation on the K₂PtCl₄ solution only (without any Co target), inwhich case no Pt NPs are formed, which confirmed that the formation ofPt NPs is largely due to the GRR.

In order to further investigate the elemental composition anddistribution in the products, EDX tests were carried out for the STEMmode images. The results from the high-angle annular dark-field (HAADF)image, as illustrated in FIGS. 12A-12D specifically for the PtCo-7sample, reveal the corresponding elemental mappings for Pt, Co and O(FIGS. 12B-12D, respectively). These images show that Pt is mainlydistributed in the bright spherical NPs in the HAADF image (i.e., thefour large NPs at the center). In contrast, Co is mostly distributed inthe background gray areas although its presence is strongly noted insidethe brighter NPs (see FIG. 12C), while O is found to be uniformlydistributed in the whole image. Furthermore, detailed EDX spectra inFIG. 12E-12F, which correspond to the areas marked e and f respectivelyin FIG. 12A indicate strong Pt and Co peaks along with weak O peakinside the bright spherical particle (FIG. 12E). In comparison, FIG. 12Fillustrates negligible Pt peak along with a relatively strong O peak inthe background areas. It is noted here that the Cu and C signals in thespectra are from the TEM carbon film with copper grids. The absence ofany other detectable elements in the EDX data indicates that all theresidual chemicals such as K₂PtCl₄ and KCl have been washed away by thecentrifuging process. The aforementioned results for the elementalmappings of Pt, Co and O in FIGS. 12B-12D, along with the EDX spectralintensities in FIGS. 12E-12F, clearly suggest the formation of PtCo NAinside the bright spherical NPs (marked as the areas e in FIG. 12A).This also validates the earlier assumption that the as-synthesized NCsare made of PtCo NA (the brighter NPs) embedded in the CoO/Co₃O₄matrices.

To corroborate the abovementioned results, FIG. 13 summarizes the XRDdata for all the PtCo/CoO_(x) NCs dispersed in CB, where the sample fromLASiS on Co (without the K₂PtCl₄ salt) displays the distinct Co₃O₄ (311)peak (PDF-#42-1467) at 2θ=36.9°, but does not show any characteristicpeak for CoO (PDF-#43-1004). In contrast, the PtCo-5 sample indicates aCoO (200) peak at 2θ=42.4° along with a minor peak at 2θ=˜36.6° which isassigned as an overlapped peak of CoO (111))(2θ=36.5° and Co₃O₄(311))(28=36.9°. These results further confirm the SAED data in FIG. 10Dthat the CoO gets partially conserved in the PtCo/CoO_(x) NCs that donot undergo further oxidation during the ageing process. Meanwhile, twodistinct characteristic peaks are also observed for this sample at2θ=40.2° and 2θ=46.7° that are assigned to the (111) and (200) peaks forPtCo alloy. Here, one needs to note that the 2θ values for standard Ptare 39.8° (111) and 46.2° (200) (PDF-#04-0802). The shift of these peaksto higher angles is attributed to the Pt alloying with Co that result ina shrunken lattice constant calculated to be approximately 3.88 Å ascompared to 3.92 Å for standard Pt. Besides, FIG. 13 also reveals thatthe alloyed PtCo peaks quickly become dominant with the increase ofPt:Co ratio. Specifically, for the case of PtCo-7 and PtCo-8 (Pt—Coratio equals to 1:2 and 1:1), the CoO_(x) peaks are barely discernable,which is ascribed to the much higher crystallinity and hence, thediffraction pattern intensity for Pt alloyed with Co as compared to thatfor CoO_(x). It needs to be noted here that this phenomenon is alsosupported by the previous SAED patterns in the insets of FIGS. 10A-D.The alloyed Pt:Co ratios from PtCo-5 to PtCo-8 are estimated to be8.6:1, 6.7:1 and 4.6:1 and 11.5:1, respectively according to theVegard's law (Equation 2), as summarized in Table 3.

TABLE 3 Sample 2θ (°) Lattice constant (Å) Pt:Co PtCo-1 40.2 3.88 8.6:1PtCo-2 40.3 3.87 6.7:1 PtCo-3 40.5 3.85 4.6:1 PtCo-4 40.1 3.89 11.5:1 

In some aspects, the seeding Co NPs from the cavitation bubble (see,e.g., 906, FIG. 9) go through two competing reactions, namely, eitherGRR with [PtCl₄]²⁺ or oxidation by solution phase O₂ and H. When theinitial K₂PtCl₄ concentration is low, a large portion of Co will reactwith solution phase O₂/H⁺, thereby leaving few available seeding Co NPsto alloy with Pt formed via GRR mediated reduction by Co. Hence, theCo:Pt ratio in the PtCo alloys rises at first with increasing initialK₂PtCl₄ concentrations in the solution. However, beyond a criticalvalue, further increase of Pt²⁺ ion concentrations leads to oxidation ofCo atoms in the initially formed PtCo alloy. Such a de-alloying processmay reduce an amount of alloyed Co in the PtCo NAs.

In some aspects, catalytic activities for both pure Co₃O₄ NPs andPtCo/Co₃O₄ NCs were tested with the aid of an RDE measurement inO₂-saturated 1M KOH solution, as shown in FIGS. 14A-14E. In order toovercome the electronic conductivity limitations and increase thecatalytic surface area for ORR experiments, all the synthesized NCs weredispersed in CB (Vulcan XC-72R, weight ratio NP:CB=1:4). Notably, LSV onpure Co₃O₄ NPs generated from high fluence (HF, 60 J/cm²) and lowfluence (LF, 1 J/cm²) LASiS has resulted in half-wave potentials anddiffusion limiting currents for HF Co₃O₄ samples that are better thanthose for LF Co₃O₄ samples (i.e., 770 mV and 3.25 mA/cm² vs. 740 mV and2.75 mA/cm² for HF vs. LF samples respectively). This is attributed tothe uniform sizes and spherical shapes of HF Co₃O₄ NPs obtained from theexplosive boiling mechanism of LASiS at high laser energy. Hence, thechoice for all catalytic studies presented herein are for the Co₃O₄ andPtCo/CoO_(x) samples synthesized at HF (60 J/cm²) conditions.

In some aspects, the clean, one-step synthesis process for LASiS may beused in generating NPs devoid of any additional chemicals (surfactants,reducing agents, etc.) that can retard or poison their catalyticactivities. FIG. 14A compares the ORR catalytic performance for each ofthe catalyst samples under study through the LSV test. The resultsindicate a remarkable improvement for the ORR activities with theincrease of Pt to Co ratio from 1:9 (PtCo-5) to 1:2 (PtCo-7).Specifically, the half-wave potential for the PtCo-7 sample is improvedto 860 mV, which is almost comparable to the corresponding values forstandard Pt/C samples (870 mV). The ORR overpotential for this sample iscalculated to be 370 mV based on the standard potential for reduction ofoxygen to water being 1.23 V. However, as the Pt:Co ratio furtherincreases to 1:1 for PtCo-8, the half-wave potential slightly reduces to850 mV, with the overpotential calculated to be 380 mV. Besides, FIG.14B compares the Tafel plots for the abovementioned samples generatedfrom FIG. 14A over the low overpotential regions. The measured Tafelslope values are 53.0, 42.2, 40.3, 39.2 and 54.6 mV/dec respectively ascompared to approximately 66.2 mV/dec for standard Pt/C samples therebyindicating higher charge transfer coefficients for the as-synthesizedcatalysts.

FIG. 14C further compares the mass activities per unit Pt loading amountat 0.85 V vs. RHE for the PtCo/CoO_(x) NCs studied. The results indicatea much higher mass activity for PtCo-7 sample (0.73 mA μg⁻¹ Pt) than thecommercial Pt/C (0.54 mA μg⁻¹ Pt). The other three samples (PtCo-5,PtCo-6 and PtCo-8) demonstrate lower but comparable mass activities,although the PtCo-8 sample with an increased amount of Pt indicates amarked drop in the ORR activity. The excellent ORR activities for thesematerials are mainly attributed to the following reasons. Firstly, theformation of alloyed PtCo nanostructures shrinks the Pt latticeconstants and decreases the effective sites for OH⁻ adsorption. Added tothat, it enhances the Pt—O bonding due to higher 5d orbital vacancies inits electronic structure that promotes the donation of π electrons fromO₂ to Pt. [30,70] Hence, the sites on the PtCo alloy NPs (known fortheir ORR activities) preferentially promote both O₂ adsorption and OH⁻desorption, both of which benefit the ORR efficiency. Secondly, the NCof the metal-transition metal oxide (NM-TMO) system further benefits theORR process by providing a synergic “spill-over” effect. [71,69]Specifically, the OH⁻ reduced from O₂ is readily desorbed from theactive PtCo sites and transferred to the sponge-shaped CoO_(x) siteswhich are less active according to their respective M-O bonding strengthand intermolecular affinities. Thus, the best ORR activity is promotedby the PtCo-7 catalyst with optimal Pt content (33.3 molar %, 62.3 wt.%) that leads to higher degree of Pt—Co alloy formation (confirmed byFIG. 13 and Table 3) with more lattice shrinkage and appropriate sizes(mean size=11.7 nm), as well as by the balanced PtCo to CoO_(x) ratiothat potentially maximizes the synergic “spill-over” effects.

In some aspects, dynamics of the electron transfer process during ORRactivities of the aforementioned catalysts are analyzed using the KLequation (Equation 4) for RDV measurements carried out at differentspeeds. For example, FIG. 14D illustrates slopes for the KL plotsgenerated from rotation-rate dependent current-potential curves (insetin FIG. 14D) for the PtCo-7 NCs in the range of 0.70-0.83 V. The slopesestimate the number of electrons transferred (n) to be 3.9-4.0, therebyindicating an ideal four-electron transport process for the ORRactivity. In some aspects, for example, a corresponding electrontransfer number for each of PtCo-5, PtCo-6 and PtCo-8 NCs is 3.8-4.0.

In addition to the good ORR catalytic activities, chronoamperometric(CA) measurements also reveal excellent stabilities for the PtCo-7 NCsamples. FIG. 14E compares the normalized current density (%) at thecorresponding half-wave potentials for the Co₃O₄, PtCo-7, and standardPt/C samples. As can be seen from the results, the ORR current densitiesdecay by less than 15% over 12000s of continuous operation for both theCo₃O₄ and PtCo-7 samples. In contrast, the standard Pt/C sampleindicates approximately a 28% current density reduction over the sameperiod of time. The decay in the catalytic activities of standard Pt/Csamples is attributed to its surface oxidation as well as particledissolution and aggregation in the alkaline electrolyte [72], whichhardly occur for the metal oxides (Co₃O₄/CoO). In fact, in the case ofthe PtCo/CoO_(x) NCs, the existence of the sponge-shaped CoO_(x) servesas a matrix material that protects the PtCo alloyed NPs from aggregationor dissolution. Meanwhile, the alloyed PtCo structure also helps to slowdown the oxidation of Pt due to the much higher electron negativity ofCo.

In some aspects, the OER catalytic activities for the PtCo NC sampleswere investigated by comparing with the results for pure Co₃O₄ andstandard Pt/C samples, as illustrated in FIGS. 15A-15B. For comparingthe OER overpotentials, all potential measurements were carried out with10 mA/cm² as the metrics due to its relevance to solar fuelcharacterizations [62]. The results reveal that, with an overpotentialof 385 mV (FIG. 15A) and a measured Tafel slope of 62.4 mV/dec, theLASiS generated Co₃O₄ itself is comparable or, even better than otherreported OER catalysts. [62, 66, 67, 68, 73, 74] As expected, thestandard Pt/C sample shows the worst OER activities (with anoverpotential of approximately 640 mV). As also mentioned earlier, thehigh OER activity for Co₃O₄ NPs is attributed to the clean synthesisroute of LASiS that produces the sponge-like nanostructures withenhanced surface area that do not have any surface contamination fromunwanted chemicals during the preparation. Notably, the most significantobservation from FIG. 15A is that the PtCo-5 sample exhibits an evensmaller OER overpotential (380 mV) than the Co₃O₄ sample that istypically well-known for OER activities. In fact, the overpotentials forPtCo-6 and PtCo-7 are also comparable (i.e., approximately 385 and 386mV respectively), indicating that these PtCo/CoO_(x) NCs exhibit goodOER catalytic activities, as well. Here, it may also be noted that thePtCo-8 sample displays a relatively poorer activity (i.e., anoverpotential of approximately 435 mV) that could be possibly due to thescarcity of CoO_(x) in the NC catalyst. It is also noted here that Tafelslopes for the PtCo NCs are slightly larger (approximately 71-72 mV/decfor PtCo-5 and PtCo-8 whereas, approximately 66-67 mV/dec for PtCo-6 and7) as compared to those for pure Co₃O₄ (approximately 62.4 mV/dec) asseen from FIG. 15B. The enhanced OER performance can also be attributedto the aforementioned synergic “spillover” effect for specific NM-TMOsystems, where the produced O₂ is desorbed from active CoO_(x) surfacesand transferred to relatively inert PtCo NA sites with higher O₂affinity. The combined overpotentials for PtCo-5 to PtCo-8 arecalculated to be 795, 775, 756, and 815 mV, respectively, whichremarkably outperform the overpotentials for either Co₃O₄ or thecommercial Pt/C (i.e., 845 mV for Co₃O₄ and 1000 mV for commercialPt/C), as shown in FIGS. 15C-15D. These results indicate that thesynthesized PtCo NCs exhibit superior bifunctional catalyticperformances for both ORR and OER processes, especially for the PtCo-7sample with an optimal Pt amount (33.3 molar %, 62.3 wt. %).

For better understanding, a schematic in FIG. 16 illustrates thedetailed mechanistic picture behind the synergic “spill-over” effectsresponsible for the site-specific adsorption/desorption of the desiredspecies to promote the bifuncitonal catalytic performances in theaforementioned NCs. For both ORR and OER, the PtCo sites and CoO_(x)matrices provide synergic support for each other wherein each of thesites provides refuge for the undesirable species from the other sites,thereby promoting both the reactions. Overall, the excellentbifunctional catalytic properties of the PtCo/CoO_(x) NCs may beattributed to the unique heteronanostructuring of alloyed PtCo NPsembedded in the sponge-shaped CoO_(x) matrices which, while contributingto the enhanced ORR and OER behaviors due to the synergic “spillover”effects, prevent the PtCo NPs from aggregation and dissolution in thealkaline media.

2.2—Synthesis of Ag Embedded ZnO/TiO₂ as Plasmonic Enhanced Materials

For the synthesis of Ag embedded ZnO/TiO₂ NCs, 5 mg of AgNO₃ was firstdissolved in 40 ml of water, then transferred into the LASiS cellthrough the injection unit, bubbled with N₂ for 30 min. The Zn/Ti pelletwas then ablated in those O₂-free AgNO₃ solutions using a laser, such asfor example, an unfocused 1064 nm laser (330 mJ/pulse, 10 Hz) for 10min. Alternatively, a laser having different configurations may beutilized. For synthesizing core-shell TiO₂/Ag NPs, right after ablation,the pH of the produced colloidal solution was adjusted to 2 by addingHNO₃ (1M) followed by aging in darkness for 24 hours and centrifuging at4700 rpm for 15 min, finally decanted after washing with DI-water fortwo times.

UV-Vis absorption measurement (Make: Biotek, Model: Synergy H1) wasscanned over the wavelength range of 300 nm to 900 nm at a scan rate of2 nm/step. The direct products from LASiS on Zn and Ti in water weredetermined as ZnO NPs, as well as a mixed state of TiO_(x) NPs,respectively. For example, FIGS. 17A-17D illustrate TEM images ofproduced ZnO NPs with irregular shapes and some degree of aggregation.In FIG. 17A, the chemical composition (oxidation state) is determined bythe SAED pattern in the inset along with the HRTEM image in FIG. 17Bthat reveals the ZnO (100) lattice plane with the d-spacing of 0.281 nm.Conversely, in FIG. 17C, two types of nanostructures are formed in theproducts of LASiS on Ti; namely, a large portion of amorphous dendriticstructure along with randomly embedded spherical NPs, which are laterdetermined as Srilankite type TiO₂ through the identification of itsd-spacing in SAED and HRTEM (reveals the (111) and (110) facets with dspacing of 0.35 nm and 0.284 nm respectively).

In some aspects, after acid wash using 10 mM HNO₃ for three hours, theamorphous TiO_(x) were completely gone, leaving only the sphericalSrilankite type TiO₂. This acid-tolerant property provides greatpotential to be applied as sensor materials or catalysts in some harshenvironment conditions.

FIG. 18A illustrates a HAADF image of the sample synthesized via LASiSon Zn in AgNO₃, while FIGS. 18B-D illustrate the corresponding Ag, Znand O EDX mappings, respectively. By carrying out tandem LASiS-GRR of Znand Ti in AgNO₃ solution, the Ag NPs are embedded into the ZnO andTiO_(x) matrices, respectively. This is also illustrated in FIGS.19A-19F, where FIG. 19A illustrates a HAADF image of the samplesynthesized via LASiS on Ti in AgNO₃ after an HNO₃ wash. FIGS. 19B-19Cillustrate an enlarged HAADF image and EDX mapping of FIG. 19A,respectively. FIG. 19D illustrates the sample illustrated in FIG. 19Aafter re-irradiation (RI) treatment. FIGS. 19E-F illustrate an enlargedHAADF image and an EDX mapping of FIG. 19D, respectively.

In some aspects, for example, for the Zn target, Ag is uniformlyembedded inside the ZnO matrices, as dictated by FIG. 18B. Bycomparison, for LASiS on Ti, as mentioned earlier, it forms a mixture ofamorphous TiO_(x) and spherical srilankite type TiO₂ NCs. For tandemLASiS-GRR on Ti with AgNO₃, an acid wash may be performed immediatelyafter, and which ends up forming core-shell Ag/srilankite TiO₂ NPs.These srilankite TiO₂ are thus confirmed to be anti-corrosive under acidconditions, which provides the possibility of their use under harshconditions. The embedding of Ag NPs is also confirmed by the XRD profileshown in FIGS. 20A-20B, where ZnO are also found to have much highercrystallinity than TiO_(x). In some aspects, (Re-irradiation) RItreatment was performed on the synthesized Ag/TiO₂ using a laser, suchas, for example, a 532 nm laser. Such an operation was found to reshapealready formed irregular shaped CoO_(x) NPs into spherical ones withenlarged sizes. Here, however, RI induces the formation of smallclusters inside the big spherical srilankite TiO₂ NPs; meanwhile, aportion of embedded Ag NPs move outwards from the edge and becomehalf-embedded, as revealed by FIGS. 19A-19F.

FIGS. 21A-21B illustrate UV-Vis absorbance. In some aspects, Ag is knownby those having skill in the art for their localized surface Plasmonresonance (LSPR) properties, which were characterized via UV-Visabsorbance. For Ag/ZnO NCs, two plasmonic peaks form with the major onelocated at approximately 440 nm and a minor one centered at 350 nm;while for the Ag/TiO_(x), the two plasmonic peaks red-shift toapproximately 500 nm and 410 nm respectively, as can be seen in FIG.21A. The dissimilarity may be due to the different Ag-metal oxideinteractions as well as the variation in sizes, which may dramaticallyimpact the electron resonance frequency and hence affect the LSPRposition. FIG. 21B illustrates the RI effect on the acid washedAg/TiO_(x) NCs. It is first noted that right after acid wash, the minorpeak at 400 nm is gone, which corresponds to the scattered Ag embeddedin the amorphous TiO_(x). However, the core-shell Ag/TiO₂ structureprotects the Ag inside from washing away by acid, and therefore, remainsthe major LSPR peak. After RI for approximately 15 and 30 min, the majorpeak slightly blue-shifts to the smaller wavelength (i.e., approximately490 nm), while the minor peak at 400 nm starts showing up again. In somecases, while it is not desired to be bound by any particular theory ofoperation, it is assumed that this is possibly ascribed to the Ag thatgradually sliding out from the TiO₂ shell—a surface re-structuringprocess exerted by laser-induced thermal and photonic energy during RI.

Example 3—Synthesis of Ternary Nanoalloys

FIG. 22A illustrates a TEM image for a sample PtCuCo-2 ternary alloysynthesized via tandem LASiS-GRR, as described herein. By carrying outtandem LASiS-GRR on Co with both K₂PtCl₄ and CuCl as metal saltprecursors, as well as applying the post treatment of acid wash andcentrifugation, PtCuCo ternary NAs with various elemental ratios areproduced. FIG. 22B illustrates the HAADF image for a sample of thePtCuCo-2 ternary alloy synthesized via tandem LASiS-GRR, as illustratedfrom FIG. 22A, while FIGS. 22C, 22E, and 22F illustrate correspondingEDX mappings of the three elements: Pt, Cu, and Co. Notably, the Coelemental distribution is not perfectly uniform. FIG. 22D illustrates aSAED image at a scale of 5 (1/nm) of the PtCuCo-2 ternary alloy. ICP-OESis used for quantifying the elemental composition of these ternaryalloys with the change of laser ablation time, as is shown in FIG. 23.

In some aspects, Co elemental composition is kept at a relative stablevalue of around 16%, while Pt and Cu exhibit a gradual increase andreduction respectively, which is probably due to already formed Cu thatgoes through further GRR with PtCl₄ ²⁻ during longer ablation time. Insome aspects, by changing the CuCl salt concentration from 0 to 0.48 mM,while keeping the K₂PtCl₄ salt concentration at around 0.3 mM andablation time at around 6 minutes, the evolution of the elementalcomposition changes are indicated in Table 4, where the Cu percentage (%at. ratio) is enhanced up to around 22% with increase in the initialCuCl quantity, whereas both Pt and Co ratio lowers down accordingly.

TABLE 4 K₂PtCl₄ Ablation time Sample (mM) CuCl (mM) (min) Pt % Co % Cu %PtCo 0.3 0 6 77 23 0 PtCuCo-1 0.03 70 24 6 PtCuCo-2 0.12 67 15 18PtCuCo-3 0.48 65 13 22

In some aspects, FIG. 24 illustrates an XRD profile for PtCuCo NAs byidentification of the Pt characteristic peak shift to higher 2-thetaangles.

REFERENCES

The references listed below as well as all references cited in thespecification are incorporated herein by reference to the extent thatthey supplement, explain, provide a background for or teach methodology,techniques and/or compositions employed herein.

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It will be understood that various details of the presently disclosedsubject matter can be changed without departing from the scope of thepresently disclosed subject matter. Furthermore, the foregoingdescription is for the purpose of illustration only, and not for thepurpose of limitation.

What is claimed is:
 1. A method for producing a metal nanoalloy and/or ametal nanocomposite using tandem laser ablation synthesis insolution-galvanic replacement reaction (LASiS-GRR), the methodcomprising: disposing a first metal composition within a reaction cell;adding a quantity of a second metal composition into the reaction cell;ablating, with a laser, the first metal composition disposed in thequantity of the second metal composition within the reaction cell; andtuning one or more reaction parameter and/or one or more functionalparameter during the tandem LASiS-GRR in order to tailor at least onecharacteristic of the metal nanoalloy and/or the metal nanocomposite. 2.The method of claim 1, wherein disposing the first metal compositionwithin the reaction cell comprises disposing a non-precious, transitionmetal as a solid metal target for ablation within the reaction cell;wherein adding the quantity of the second metal composition into thereaction cell comprises injecting into the reaction cell a quantity of asolution of one or more precious metal salt precursor chosen to bear ahigher redox potential than the non-precious, transition metal target;and wherein ablating, with the laser, the first metal compositiondisposed in the quantity of the second metal composition within thereaction cell comprises ablating, with a high-energy, pulsed laser, thenon-precious, transition metal target disposed in the quantity of thesolution of one or more precious metal salt precursor inside thereaction cell, while the non-precious, transition metal target iscontinuously rotated for uniform ablation.
 3. The method of claim 1,wherein the one or more functional parameter is selected from the groupconsisting of simultaneous ultra-sonication, controlled chemicalinjection, rotation of the first metal composition, and controlledtemperature and environmental gas for the reaction cell; and wherein theone or more reaction parameter is selected from the group consisting oflaser parameters comprising laser energy (fluence), laser wavelength,and a period of time the laser is configured to ablate the first metalcomposition, and environmental parameters comprising an initial quantityof a solution of the second metal composition in the reaction cell, anda solution phase pH condition.
 4. The method of claim 1, furthercomprising producing a metal nanocomposite comprising a substantiallyuniform alloyed core of a first metal of the first metal composition anda second metal of the second metal composition, and a shell or matrixsurrounding the substantially uniform alloyed core, the shell or matrixcomprising an oxide of one of the first metal and the second metal. 5.The method of claim 1, wherein the at least one characteristic comprisesa size, a shape, a structure, and/or a composition of the metalnanoalloy and/or the metal nanocomposite.
 6. The method of claim 1,wherein the metal nanoalloy is a binary metal nanoalloy selected fromthe group consisting of PtCo, PtNi, PtCu, and PdCo.
 7. The method ofclaim 1, wherein the metal nanocomposite is a binary metal nanocompositeselected from the group consisting of PtCo/CoOx, PdCo/CoOx, Ag/ZnO, andAg/TiOx.
 8. The method of claim 1, wherein the metal nanoalloy is aternary metal nanoalloy selected from the group consisting of PtCuCo,PtCoMn, and PtCoNi.
 9. The method of claim 1, wherein the metalnanoalloy is stable under acidic and/or alkaline conditions.
 10. A metalnanoalloy and/or metal nanocomposite produced by the method of claim 1.11. A system for producing a metal nanoalloy and/or a metalnanocomposite using tandem laser ablation synthesis in solution-galvanicreplacement reaction (LASiS-GRR), the system comprising: a reactioncell; a first metal composition disposed within the reaction cell; aquantity of a second metal composition configured to be added into thereaction cell; and a laser configured to ablate the first metalcomposition disposed in the quantity of the second metal compositionwithin the reaction cell, wherein the system is configured such that oneor more reaction parameter and/or one or more functional parameter istuned during the tandem LASiS-GRR in order to tailor at least onecharacteristic of the metal nanoalloy and/or the metal nanocomposite.12. The system of claim 11, wherein the first metal compositioncomprises a non-precious, transition metal as a solid metal target forablation; wherein the quantity of the second metal composition comprisesa quantity of a solution of one or more precious metal salt precursorchosen to bear a higher redox potential than the non-precious,transition metal target and configured to be injected into the reactioncell; and wherein the laser comprises a high-energy, pulsed laserconfigured to ablate the non-precious, transition metal target disposedin the quantity of the solution of one or more precious metal saltprecursor inside the reaction cell, while the non-precious, transitionmetal target is continuously rotated for uniform ablation.
 13. Thesystem of claim 11, wherein the one or more functional parameter isselected from the group consisting of simultaneous ultra-sonication,controlled chemical injection, rotation of the first metal composition,controlled temperature and environmental gas for the reaction cell; andwherein the one or more reaction parameter is selected from the groupconsisting of laser parameters comprising laser energy (fluence), laserwavelength, and a period of time the laser is configured to ablate thefirst metal composition, and environmental parameters comprising aninitial quantity of a solution of the second metal composition in thereaction cell, and a solution phase pH condition.
 14. The system ofclaim 11, wherein the metal nanocomposite comprises a substantiallyuniform alloyed core of a first metal of the first metal composition anda second metal of the second metal composition, and a shell or matrixsurrounding the substantially uniform alloyed core, the shell or matrixcomprising an oxide of one of the first metal and the second metal. 15.The system of claim 11, wherein the at least one characteristiccomprises a size, a shape, a structure, and/or a composition of themetal nanoalloy and/or the metal nanocomposite.
 16. The system of claim11, wherein the metal nanoalloy is a binary metal nanoalloy selectedfrom the group consisting of PtCo, PtNi, PtCu, PdCo
 17. The system ofclaim 11, wherein the metal nanocomposite is a binary metalnanocomposite selected from the group consisting of PtCo/CoOx,PdCo/CoOx, Ag/ZnO, and Ag/TiOx.
 18. The system of claim 11, wherein themetal nanoalloy is a ternary metal nanoalloy selected from the groupconsisting of PtCuCo, PtCoMn, and PtCoNi.
 19. A metalheteronanostructure comprising: a substantially uniform alloyed core ofa first metal and at least one second metal; and a shell or matrixsurrounding the substantially uniform alloyed core, the shell or matrixcomprising one of the first metal and the at least one second metal. 20.The metal heteronanostructure of claim 19, wherein the shell or matrixcomprises an oxide of one of the first metal and the at least one secondmetal such that the metal heteronanostructure is a metal nanocomposite.21. The metal heteronanostructure of claim 19, wherein the at least onesecond metal has a higher redox potential than the first metal.
 22. Themetal heteronanostructure of claim 21, wherein the first metal comprisesa non-precious, transition metal and the at least one second metalcomprises at least one precious metal having a higher redox potentialthan the non-precious, transition metal.
 23. The metalheteronanostructure of claim 22, wherein the shell or matrix surroundingthe substantially uniform alloyed core comprises the non-precious,transition metal.
 24. The metal heteronanostructure of claim 19, whereinthe metal heteronanostructure is produced using tandem laser ablationsynthesis in solution-galvanic replacement reaction (LASiS-GRR).
 25. Themetal heteronanostructure of claim 24, wherein at least onecharacteristic of the metal heteronanostructure is configured to betailored during the tandem LASiS-GRR by tuning one or more reactionparameter and/or one or more functional parameter during the tandemLASiS-GRR.
 26. The metal heteronanostructure of claim 25, wherein the atleast one characteristic comprises a size, a shape, a structure, and/ora composition of the metal heteronanostructure.
 27. The metalheteronanostructure of claim 19, wherein the metal heteronanostructureis a binary nanocomposite selected from the group consisting ofPtCo/CoOx, PdCo/CoOx, Ag/ZnO, and Ag/TiOx.
 28. The metalheteronanostructure of claim 19, wherein the substantially uniformalloyed core comprises a uniform precious metal to at least onenon-precious, transition metal ratio, with a non-precious transitionmetal percentage ranging from 0-38%.
 29. The metal heteronanostructureof claim 19, wherein the metal heteronanostructure is stable underacidic and/or alkaline conditions.
 30. The metal heteronanostructure ofclaim 19, wherein the metal heteronanostructure is a binary metalnanoalloy selected from the group consisting of PtCo, PtNi, PtCu, andPdCo.
 31. The metal heteronanostructure of claim 19, further comprisinga third metal, wherein the substantially uniform alloyed core comprisesthe first metal, the second metal, and the third metal; and the shell ormatrix surrounding the substantially uniform alloyed core comprises oneor more of the first metal, the second metal, and the third metal. 32.The metal nanocomposite of claim 31, wherein the third metal has ahigher redox potential than the first metal, the second metal, or boththe first metal and the second metal.
 33. The metal heteronanostructureof claim 19, wherein the metal heteronanostructure is a ternary metalnanoalloy selected from the group consisting of PtCuCo, PtCoMn, andPtCoNi.
 34. The metal heteronanostructure of claim 19, wherein the metalheteronanostructure comprises a degree of alloying approximately between40-60%.
 35. The metal heteronanostructure of claim 19, wherein the metalheteronanostructure comprises a mean crystallite size approximatelybetween 3-18 nm.
 36. The metal heteronanostructure of claim 19, whereinthe metal heteronanostructure comprises shrinkage in lattice constantapproximately between 0 to 2.4%.
 37. A substantially uniform nanoalloycomprising: a first metal; and at least one second metal, wherein thefirst metal is a precious metal and the second metal is a non-precious,transition metal, and wherein a degree of alloying is approximatelybetween 40-60%.
 38. The substantially uniform nanoalloy of claim 37,wherein the precious metal is Pt and the non-precious, transition metalis Co.
 39. The substantially uniform nanoalloy of claim 37, wherein thesubstantially uniform nanoalloy comprises a mean crystallite sizeapproximately between 1-20 nm.
 40. The substantially uniform nanoalloyof claim 37, wherein the substantially uniform nanoalloy comprises ashrinkage in lattice constant approximately between 0-2.4%.
 41. Thesubstantially uniform nanoalloy of claim 37, wherein the first metalcomprises a non-precious, transition metal and the at least one secondmetal comprises at least one precious metal having a higher redoxpotential than the non-precious, transition metal.
 42. The substantiallyuniform nanoalloy of claim 37, further comprising a third metal.
 43. Thesubstantially uniform nanoalloy of claim 42, wherein the third metal hasa higher redox potential than the first metal, the second metal, or boththe first metal and the second metal.
 44. The substantially uniformnanoalloy of claim 37, wherein the nanoalloy is a binary metal nanoalloyselected from the group consisting of PtCo, PtNi, PtCu, and PdCo. 45.Substantially uniform nanoalloy of claim 42, wherein the nanoalloy is aternary metal nanoalloy selected from the group consisting of PtCuCo,PtCoMn, and PtCoNi.
 46. A catalyst composition comprising a metalheteronanostructure of claim
 19. 47. A catalyst composition comprising asubstantially uniform nanoalloy of claim 37.